HIGHWAY   INSPECTORS' 
HANDBOOK 


WORKS  OF 
PROVOST  HUBBARD 

CHEMICAL    ENGINEER 

Published  by 
JOHN  WILEY  AND  SONS,  INC. 

Highway  Inspectors'  Handbook.     A  book  for   the  field 
use  of  Inspectors,  Engineers  and  Contractors, 
xxvi  +  372  pages,  4|  X  7,  55  figures.    Cloth,  $2.50  net. 

Laboratory  Manual  of  Bituminous  Materials.      A  man- 
ual for  the  use  of  Students  in  Highway  Engineering, 
Chemists  and  Testing  Engineers. 
vii  +  153  pages,  6  X  9,  39  figures.    Cloth,  $1.50  net. 

Dust    Preventives    and    Road    Binders.     A    book    for 
Students,  Engineers  and  Contractors. 
vi  +  416  pages,  6  X  9,  51  figures.  Cloth,  $4.00  net. 

Section  12,  "Bituminous  Materials",  in  American   High- 
way Engineers'  Handbook. 


HIGHWAY  INSPECTORS' 
HANDBOOK 


BY    • 

PREVOST  HUBBARD 

CHEMICAL   ENGINEER,    THE    ASPHALT   ASSOCIATION 

FORMERLY   CHIEF,    DIVISION   OF   ROAD   MATERIAL   TESTS    AND    RESEARCH, 
BUREAU     OF     PUBLIC     ROADS,     U.     S.     DEPARTMENT     OF     AGRICULTURE 


TOTAL  ISSUE 
FOUR  THOUSAND 


NEW  YORK 

JOHN    WILEY    AND    SONS,    INC. 


• 


LONDON:  CHAPMAN  AND  HALL,  LIMITED 

iSS     Market  St, 

1919 


i 


COPYRIGHT,     igig 
BY    PREVOST    HUBBARD 


t8>108    ( 
,JJAH 


4-21 


- 

• 


PREFACE 

4  LTHOUGH  this  handbook  has  been  prepared  primarily 
-LA.  for  the  use  of  inspectors,  it  is  hoped  that  it  may  also 
prove  of  service  to  engineers  and  contractors.  The  author 
has  endeavored  to  present  most  of  the  important  details  of 
highway  construction  and  maintenance,  as  briefly  as  possible, 
in  such  form  as  to  be  quickly  available  to  the  Inspector,  who 
wishes  to  be  told  what  to  do  rather  than  what  others  have 
done  under  various  conditions.  It  has,  of  course,  been 
necessary  to  include  considerable  explanatory  matter  in  order 
that  he  may  follow  directions  and  suggestions  intelligently. 

In  place  of  tables,  so  commonly  found  in  most  handbooks, 
the  author  has  made  use  of  a  large  number  of  diagrams  in 
order  to  save  space  and  present  data  in  convenient  form  for 
field  use.  These  diagrams  have  been  prepared  from  the  most 
reliable  data  that  he  has  been  able  to  secure,  from  his  own 
experience  and  from  various  records  of  work  done  through- 
out the  country.  On  some  subjects,  however,  the  available 
information  is  very  limited,  and  criticisms  and  comments 
will  be  appreciated  from  engineers  who  may  have  occasion 
to  refer  to  certain  of  these  diagrams  and  find  that  the  values 
given  vary  from  their  own  experience  under  a  given  set  of 
conditions. 

Throughout  the  volume,  each  general  subject  has  been 
divided  into  articles,  numbered  consecutively,  and  frequent 
cross  references  will  be  found  to  articles  in  other  parts  of  the 
book.  All  cross  references  are  indicated  in  the  text  by  the 
insertion  of  an  article  number  in  parenthesis. 

It  is  realized  that  the  field  of  highway  engineering  has  been 
well  covered  by  a  number  of  excellent  text  and  reference 
books,  but  the  subject  of  adequate  inspection  has  never  been 

7089&0 


vi  Preface 

dealt  with  as  fully  as  its  importance  warrants.  Many  costly 
failures  in  the  past  would  undoubtedly  have  been  prevented 
had  the  work  received  proper  and  intelligent  inspection. 
Much  unsatisfactory  work  in  the  future  will  be  prevented  if 
adequate  inspection  is  furnished.  It  is  hoped,  therefore, 
that  this  little  volume  will  meet  a  real  need  in  the  profession 
of  highway  engineering. 

PBEVOST  HUBBARD 
May  19,  1919 


uro'il 


rifj  fi^  16 


TABLE  OF  CONTENTS 

A.PTER  PAGE 

I.  HIGHWAY  INSPECTION 1 

II.  BROKEN  STONE .12 

III.  GRAVEL,  SAND  AND  CLAY 32 

IV.  HYDRAULIC  CEMENT 47 

V.  BITUMINOUS  MATERIALS 58 

VI.    LABORATORY    TESTS    OF  BITUMINOUS  MA- 
TERIALS           ....        86 

VII.  INSPECTION  OF  SAND-CLAY,  GRAVEL,  SHELL 

AND  SHOVEL-RUN  OR  CRUSHER-RUN  SLAG 
ROADS 103 

VIII.  INSPECTION  OF  BROKEN  STONE  AND  BROKEN 

SLAG  ROADS 121 

IX.    INSPECTION  OF  BITUMINOUS  SURFACE  TREAT- 
MENTS       138 

X.    INSPECTION    OF    BITUMINOUS    MACADAM 

PAVEMENTS 151 

XI.    INSPECTION     OF    CONCRETE    FOUNDATIONS 

AND  PAVEMENTS 165 

BITUMINOUS  PAVING  PLANT  INSPECTION      .      189 
INSPECTION  OF  BITUMINOUS  CONCRETE  AND 

SHEET  ASPHALT  PAVEMENTS  .      .      .      .      212 
£IV.    INSPECTION  OF  BRICK  AND    BLOCK    PAVE- 
MENTS        250 

XV.    INSPECTION  OF  MISCELLANEOUS  WORK  AND 

MATERIALS .      .      283 

MEASUREMENTS ^  300 

MISCELLANEOUS  FIELD  TESTING  AND  SAMP- 
LING EQUIPMENT 324 

RECORDS  AND  REPORTS 346 

TYPICAL  MATERIAL  REQUIREMENTS       .      .      357 

INDEX 363 

vii 


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INDEX  OF  ARTICLES 


I.   HIGHWAY  INSPECTION 

AETICLE  PAGE 

THE  INSPECTOR: 

1.  Highway  Inspection 1 

2.  Qualification  of   Inspectors 1 

3.  Responsibility    of  Inspectors " 2 

CLASSES  OF  INSPECTION: 

4.  Laboratory  Inspection 3 

5.  Plant  Inspection 3 

6.  Roadside  Inspection 4 

RELATIONS  OF  THE  HIGHWAY  INSPECTOR: 

7.  The  Engineer 5 

8.  The  Laboratory 6 

9.  The  Contractor 7 

SPECIFICATIONS  : 

10.  General  Scope  of  Specifications 8 

11.  Basis  of  Measurement  and  Payment 9 

12.  Cooperation  of  Contractor  on  Inspection. 9 

13.  Inspection  Details 10 

14.  Removal  and  Replacement  of  Work 10 

II.   BROKEN   STONE 

ROCK: 

15.  Occurrence 12 

16.  Classification. 12 

17.  Manufacture  of  Broken  Stone 14 

. 

PHYSICAL  PROPERTIES: 

18.  Specification  Requirements 15 

19.  Important  Rock-forming  Minerals 16 

20.  Trap  Rock 18 

21.  Granite  and  Gneiss 18 

22.  Limestone 19 

23.  Sandstone  and  Quartzite 19 

ix 


x  Index  of  Articles 

ARTICLE  PAGE 

24.  Chert 19 

25.  Fieldstone  and  Conglomerates 20 

26.  Schist,  Shale  and  Slate 20 

27.  Relative  Properties  of  Important  Rocks 20 

ROCK  TESTS: 

28.  Resistance  to  Abrasion  or  Wear 22 

29.  Toughness 23 

30.  Hardness 23 

31.  Cementing  Value 24 

32.  Size  or  Grading 24 

33.  Specific  Gravity,  Weight  per  Cubic  Foot,  Absorption 24 

34.  Determination  of  Voids 25 

MEASUREMENT  : 

35.  Weight  Basis 26 

36.  Volume  Basis 26 

37.  Voids 27 

SAMPLING  : 

38.  Time  and  Place  of  Sampling . , 29 

39.  Sampling  for  Quality 30 

40.  Sampling  for  Size  or  Grading 31 


III.   GRAVEL,   SAND  AND  CLAY 

NATURAL  ROCK  PRODUCTS: 

41.  Occurrence 32 

42.  Classification ??!'!??.. 32 

GRAVEL: 

43.  Typesof Gravel 33 

44.  Production , 34 

45.  Physical   Properties ".TiT^',.  .;V.  34 

SAND: 

46.  Types  of  sand .m«*nr>r- 36 

47.  Production 37 

48.  Physical  Properties 37 

CLAY: 

49.  Types  of  Clay 40 

50.  Properties 41 


Index  of  Articles  xi 

ARTICEE  .  PAGE 

TESTS: 

51.  Resistance  to  Abrasion  or  Wear 41 

52.  Cementing  Value 42 

53.  Washing  and  Elutriation  Tests 42 

54.  Size  or  Grading 43 

55.  Washing  Test  and  Grading  of  Top  Soil  and  Sand  Clay 43 

56.  Specific  Gravity 44 

57.  Determination  of  Voids 44 

58.  Mortar  Tensile  Strength  Test  for  Sand 44 

SAMPLING: 

59.  Time  and  Place  of  Sampling 45 

60.  Methods  of  Sampling 45 

IV.  HYDRAULIC  CEMENTS 

GENERAL  CHARACTERISTICS: 

61.  Classification 47 

62.  Manufacture 47 

63.  Properties 48 

SPECIFICATIONS  FOR  PORTLAND  CEMENT 

64.  Standardization 48 

65.  Definition 49 

66.  Chemical  Properties 49 

67.  Physical   Properties 49 

68.  Packages,  Marking  and  Storage 50 

69.  Inspection 50 

70.  Rejection 50 

SPECIFICATIONS  FOR  NATURAL  CEMENT: 

71.  Standardization 51 

72.  Definition 51 

73.  Physical  Properties 51 

74.  Packages,  Marking  and  Storage 52 

CEMENT  TESTS: 

75.  Chemical  Analysis 52 

76.  Specific  Gravity 

77.  Fineness 53 

78.  Normal  Consistency 53 

79.  Soundness 54. 

80.  Time  of  Setting 54 

81.  Mortar  Tensile  Strength 54 

82.  Tensile  Strength  Neat  Cement 55 


xii  Index  of  Articles 

ARTICLE  PAGE 

MEASUREMENT: 

83.  Basis  of  Purchase. ...... :»?.  7?  ™.¥?'rff.°*  K??:^-.11.1.       55 

84.  Volume  and  Weight  Relations ...  ;?V/^Y.  ??f '/V3.".1. .;'.       55 

SAMPLING: 

85.  Time  and  Place  of  Sampling ...;;... ..'-> .  & . ......       56 

86.  Methods  of  Sampling •.!>-.. :........       57 


V.   BITUMINOUS   MATERIALS 

GENERAL  CHARACTERISTICS: 

87.  Composition  .........  ...........  .../.....  .....  .......  58 

88.  Classification  ................................  .......'.  58 

89.  Manufacture.  .,./-.{.?,/.  T...  .  .  .....  ffH-VH-  v/f  ...........  59 

90.  Temperature  Control  .................................  59 

91.  Effect  of  Water  .....................  '.'  Pr'/l'!'™5!^?.  :v;  60 

92.  Transportation   and   Storage  ..............  ^'Jl'PJl';--.  J.  :  61 

,-)H  J-.,;'tlJjij;f  /.  <'•'• 

PETROLEUM  AND  ASPHALT  PRODUCTS: 

'  93.   Types  of  Petroleum.  .  .  .  ,  .„.,.,,  ,,,..,       f  •i>m-^-,  62 

94.  Petroleum  Distillates  .....................  ........  v  ..,.  63 

95.  Liquid  Petroleum  Residues  .............  •.'!(.".r!!?  I.lTT/">.M/iIri.  63 

96.  Asphalts  and  Asphalt  Cements.  .........:...  //VV!1.3-'?'.'?.  64 

97.  Asphalt  Fillers.  .....  .........  .  .....  ™*?W*\  .^?^I?'J').  66 

98.  Cut-back  Asphalts  ....  .....  .:..:...  ^JT.1^  -  !':'!';  <:N.  66 

1  "99.   Emulsions  and  Emulsifying  6ife  ;  !.1  h!V'.  S^™1?.  ».^f  ™!J  '''  66 

100.  Rock  Asphalt  .....  .  ....................  .  .  ;  .  :a™*?.  b7 

.....    noit->'»i'-.Jl 

TAR  PRODUCTS: 

:Tx:u/:-i  J  .i/jrjT/  /:  ao'i  Hxorr/.'jf-ir  >.!••,". 

101.  Types  of  Tar  ....                           .........           •„        ^  68 

102.  Liquid  Refined  Tars  ......  ...............  ...'.'/.,  A  ..  .(  }.  .70 


pn 

104.   Pitch  Fillers 


.  ...... 

ir._     0.         ,.  _..  .i>Hino!fff>iujaai^i>sl/:  fV)J|JiJJ-)/:*ip 

105.   Creosoting  Oils  ...........  .  .........  .  .  ........  ;......       71 

MEASUREMENT  : 


!n-)ii«i'.«fi  )  .c,  . 

106.  Weight  Basis  ........................  .-^rwrO  -)ih-  -  -  -  •  71 

107.  Volume   Basis.  ...  ...............  ......'.........  .....  73 

108.  Temperature  Corrections  of  Volume  ....................  ,^~77 

SAMPLING: 

109.  Time  and  Place  of  Sampling.  .  80 

110.  Size  of  Samples.  .  ..............  .  .....................  80 

111.  Containers..  81 


Index  of  Articles  xiii 

ARTICLE  PAGE 

112.  General  Precautions 81 

113.  Sampling  from  Pipe  Lines 82 

114.  Sampling  Directly  from  Tanks 82 

115.  Sampling  from  Barrels  and  Drums 83 

116.  Sampling  from  Loose  Bulk 84 

117.  Prepared  Joint  Fillers 85 

VI.   LABORATORY  'TESTS   OF    BITUMINOUS    MATERIALS 

SIGNIFICANCE  OF  LABORATORY  TESTS: 

118.  Value  of  Tests 86 

119.  Specification  Requirements 86 

120.  Temperature   Considerations 87 



DENSITY  TESTS: 

121.  Specific  Gravity 88 

122.  Coefficient  of  Expansion .  . 91 

CONSISTENCY  TESTS: 

123.  Viscosity 91 

124.  FloatTest 9 

125.  Penetration  Test 

126.  Melting  or  Softening  Point 94 

127.  Ductility 95 

HEAT  TESTS: 

128.  Flash  and  Burning  Points 95 

129.  Volatilization  Test 96 

130.  Asphalt  Contents 97 

131.  Determination  of  Water : 97 

132.  Distillation 97 

SOLUBILITY  TESTS: 

133.  Total  Bitumen 98 

134.  Asphaltenes,  or  Bitumen  Insoluble  in  Paraffin  Naphtha ....  99 

135.  Carbenes  or  Bitumen  Insoluble  in  Carbon  Tetrachloride ..  100 

136.  Dimethyl  Sulphate  Test 100 

MISCELLANEOUS  TESTS: 

137.  Fixed  Carbon 101 

138.  Paraffin  Scale 101 

139.  Special  Tests  for  Emulsion. . 

140.  Special  Tests  for  Creosoting  Oils 102 


xiv  Index  of  Articles 

VII.  INSPECTION  OF  SAND-CLAY,   GRAVEL,   SHELL     AND 
SHOVEL-RUN  OR  CRUSHER-RUN  SLAG  ROADS 

ARTICLE  PAGE 

SAND-CLAY  AND  TOPSOIL  ROADS: 

141.  General  Characteristics .:..... 103 

142.  Construction  Methods 104 

143.  Selection  of  Materials 104 

144.  Field  Tests  of  Materials T  . .  . . ,  v ;. v  . , 105 

145.  Measurements 107 

146.  Sampling .: 108 

147.  Inspector's  Equipment /.  109 

GRAVEL  ROADS: 

148.  General  Characteristics 110 

149.  Construction  Methods Ill 

150.  Material  Requirements 112 

151.  Field  Tests  of  Materials...  .  ...  .  ...,;..?.v  ,.;./.  _.,hf^,.'  113 

152.  Measurements 114 

153.  Sampling 116 

154.  Inspector's  Equipment , .  117 

SHELL  ROADS: 

155.  General  Characteristics '.'..'. . .. . . . '..'".  fj.[ . . . . .'.  1 1 .  117 

156.  Inspection ..".".  l.°.'?|"| \  .'^ .  118 

SHOVEL-RUN  OR  CRUSHER-RUN  SLAG  ROADS: 

157.  General  Characteristics '.".  \ ".  \  1  _.  "   119 

158.  Inspection ;  I .  V1.!1!1!  V'A1.  !)J.!.I!.  ^:(  1 .  119 

cH? f^-jT  noftj',\i{i  jjilo  /    .i.'Lf 

MAINTENANCE: 

159.  General  Methods -»\*H'U  •  u>  «*w  \niiaw wk.1  •  119 

160.  Inspection  of  Maintenance -jad^aif&siO.  120 

VIII.  INSPECTION  OF  BROKEN  STONE  AND  BROKEN 

SLAG  ROADS 
GENERAL  CHARACTERISTIC^:11' 

161    Definition  121 

121 


162.  Types .'.  /.'VV?!1.' 'Y.V1/:"/!' 

163.  General  Methods  of  Construction -r-iv.M.'F  •auAa> 122 

IMPORTANT  DETAILS  OP  MACADAM  CONSTRUCTION: 

164.  Preparation  of  Subgrade 123 

165.  Spreading  the  Stone  or  Slag • 124 

166.  Compacting  and  Bonding  the  Courses 125 


Index  of  Articles  xv 

ARTICLE  PAGB 

MATERIALS: 

167.  Rock   126 

168.  Slag. . ................'..'..'.  127 

169.  Sizes  of  Commercial  Products 128 

170.  Field  Tests ...........  130 

171.  Measurements 131 

172.  Sampling 134 

MAINTENANCE  : 

173.  Methods. 135 

174.  Inspection 136 

INSPECTOR'S  EQUIPMENT: 

175.  Telford  Roads 136 

176.  Macadam    Roads 137 


IX.  INSPECTION  OF  BITUMINOUS  SURFACE  TREATMENTS 

GENERAL  CHARACTERISTICS: 

177.  Definition 138 

178.  Types 138 

IMPORTANT  DETAILS  OF  SURFACE  TREATMENT: 

179.  Preparation  of  Road  Surface 139 

180.  Application  of  Bituminous  Material 140 

181.  Application  of  Mineral  Cover 142 

. 

MATERIALS: 

182.  Dust  Preventives 143 

183.  Carpeting  Mediums 144 

184.  Mineral  Cover 145 

185.  Field  Tests 146 

186.  Measurements 146 

187.  Sampling 149 

MAINTENANCE  : 

149 




189.  Inspection 150 

INSPECTOR'S  EQUIPMENT: 

190.  Treatment  With  Dust  Preventives 150 

191.  Treatment  with  Carpeting  Medium 150 


xvi  Index  of  Articles 

X.   INSPECTION  OF  BITUMINOUS  MACADAM  PAVEMENTS 

ARTICLE  PAGE 

GENERAL  CHARACTERISTICS: 

192.  Definition „.., „;,.,,;.(.'.;„,. _nr  ...;. , . , ", . . .  151 

193.  Usual  Method  of  Construction j .  ,.,. ...;.'  151 

DETAILS  OF  CONSTRUCTION: 

194.  Foundations ; .......... 152 

195.  Spreading  and  Compacting  Coarse  Stone ,:  ys.s  v  .i.  152 

196.  First  Application  of  Bituminous  Material .  .< . ,;/.  153 

197.  Filling   Surface  Voids .,,  ,.?;r,,,rf.  155 

198.  Seal  Coat. '..'. ! ... .  155 

MATERIALS: 

.199.   BrokenStone. . . 7 f.  .^.,|:?:.  ... . . '.,.).  156 

200.  Broken  Slag. . "?':?..  /./::.  .  .'!  .  156 

201.  Asphalt  Cement 157 

202.  Refined  Tar.,r;.  JT^pje  ^lJOXIM'!-TlH-'*i<  '  vlOI'T'-)^! ':•/•;  158 

203.  Field  Tests. . . . . . . '. . . . .".... ...'...  159 

204.  Measurements ..,...,. .,, ,,.,  ir  . .  }f ..  159 

205.  Sampling '...'... , '.  ".'  161 

........  noninnoCl 

MAINTENANCE  : 

206.  Methods. 162 

™T      n/r    A      •    i                       .TX3MTA3HJ     /i'V.  ,  co 

207.  Materials 163 

INSPECTOR'S  EQUIPMENT:      i^^ 

208.  Construction.  ....... ..... ......... ,-K»:/<>-  '  i«T>iHjjC''i<>ri«s)ili:oii<{<|!/i  •  163 

209.  Maintenance.  .  164 


XI.   INSPECTION  OF  CONCRETE  FOUNDATIONS  AND 

PAVEMENTS 

1-j/o')  k-»n|M   .i-XJ 

GENERAL  CHARACTERISTICS: 

210.  Composition -.^iwHifctrtM  •  ..165 

211.  Proportioning. r3«Hqiiijjfc.     165 

212.  Properties 166 

213.  Types  of  Construction 166 

IMPORTANT  DETAILS  OF  CONSTRUCTION  : 

.  . 

214.  Preparation  of  Subgrade 167 

215.  Proportions 167 

216.  Mixing >  .>;.;n.v 170 

217.  Consistency * 171 


Index  of  Articles  xvii 

ARTICLE  PAGE 

218.  Placing  and  Shaping 171 

219.  Finishing  the  Surface 173 

220.  Curing 174 

MATERIALS  : 

221.  Cement 174 

222.  Coarse  Aggregate 174 

223.  Fine  Aggregate : ' 176 

224.  Water 178 

225.  Reinforcing   Metal 178 

226.  Hydrated  Lime 178 

227.  Materials  for  Expansion  Joints 179 

228.  Field  Tests 179 

229.  Measurements . 180 

230.  Sampling 183 

MAINTENANCE  OF  CONCRETE  PAVEMENT: 

,,    ,     , 

231.  Methods 185 

232.  Inspection 186 

INSPECTOR'S  EQUIPMENT: 

«oo         n            x             .•                        '            •  •«,-,/•. 

233.  Construction 186 

«0,             AT       •        ,  StC, 

234.  Maintenance 188 

• 


XII.   BITUMINOUS   PAVING  PLANT   INSPECTION 

PAVING  PLANTS: 

235.  Function  of  Paving  Plants 189 

236.  Duties  of  Plant  Inspector 190 

237.  Types  of  Plants ' 190 

PLANT  OPERATION: 

238.  Storage    of    Materials 192 

239.  Heating  Mineral  Aggregates 193 

240.  Separating  the  Aggregate 193 

241.  Heating  and  Fluxing  Bituminous  Materials 194 

242.  Proportioning  the  Constituents  of  the  Mix 195 

243.  Mixing 195 

244.  Transportation  of  Mix  to  the  Road 196 

INSPECTION  DETAILS: 

245.  Characteristics  of  Mineral  Constituents 196 

246.  Consistency  and  Bitumen  Content  of  Bituminous  Material  197 

247.  Control  of  Temperatures 201 


xviii  Index  of  Articles 

ARTICLE  PAGE 

248.  Measurement  and  Control  of  Proportions < .  ,, , . , . . 202 

249.  The  Combination  of  Aggregates 205 

250.  Characteristics  of  Mix 208 

251.  Output  of  the  Plant 209 

252.  Cooperation  of  Inspectors 209 

INSPECTOR'S  EQUIPMENT: 

253.  The  Plant  Laboratory 210 

254.  Personal  Equipment 211 


XIII.   INSPECTION  OF  BITUMINOUS   CONCRETE  AND 
SHEET    ASPHALT  PAVEMENTS 

GENERAL  CHARACTERISTICS: 

255.  Types  of  Pavement r,.  r.M,  . ., .... 212 

256.  General  Method  of  Construction ...  213 

DETAILS  OF  CONSTRUCTION  APPLICABLE  TO  ALL  TYPES: 

257.  Foundations r/'lft'j '  HV!' ' '  •'•  •  •  213 

258.  Preparation  of  the  Bituminous  Aggregate , 214 

259.  Function  and  Characteristics  of  Mineral  -Filler ! ".".  t.'."?:-:;!<: .'.  215 

260.  Spreading  the  Bituminous  Aggregate.  .....;.''/!?!':  V '.'..:.  216 

261.  Compacting  and  Finishing 217 

262.  Measurement. . : .':  { :  l'.f .  .' .* '{-. '.  { (\  1.7.  V.'.7: 11-//.'!1.1?/ . : '.'/.  .  219 

263.  Sampling 220 

ONE  SIZE  STONE  BITUMINOUS  CONCRETE: 

264.  The  Mineral  Aggregate .  .'j..ty v^-.'ul .  uiulU.  .tu.  ?j'm,il .  220 

265.  The  Bituminous  Material '...  .>.-iu;W  .to.  .*j.v.  t  •  221 

266.  TheMix 

267.  The  Seal  Coat .f 

COARSE  GRADED  AGGREGATE  BITUMINOUS  CONCRETE: 

268.  The  Coarse  Aggregate. .AJ/jy-.rj^u'wiXyiJUf/Juq'^.  225 

269.  The  Fine  Aggregate.  . .  .  fcuoniauitj ifait/jyji  .  226 

270.  The  Bituminous  Material ariJ.anijKuJ-ioqot^  .  227 

271.  The  Mix ym,-; ...  227 

272.  The  Seal  Coat 230 

FINE  GRADED  AGGREGATE  BITUMINOUS  CONCRETE     (TOPEKA  TYPE): 

273.  The  Broken  Stone  Aggregate 230 

274.  The  Sand  Aggregate 231 

275.  The  Asphalt  Cement 231 


Index  of  Articles  xix 

ABTICLE  PAGE 

276.  The  Mix 232 

277.  Paint  Coats. 236 

SHEET  ASPHALT: 

278.  The  Binder  Course 236 

279.  The  Sand  Aggregate  for  Topping 238 

280.  The  Asphalt  Cement 240 

281.  The  Topping  Mix 241 

ROCK  ASPHALT  PAVEMENTS: 

282.  Bituminous  Sandstone 243 

283.  Bituminous  Limestone 244 

BITUMINOUS  EARTH  PAVEMENTS: 

284.  The  Mineral  Aggregate 244 

285.  The  Asphalt  Cement 245 

286.  The  Mix 246 

MAINTENANCE: 

287.  Methods 246 

288.  Inspection 247 

INSPECTOR'S  EQUIPMENT: 

289.  Construction 248 

290.  Maintenance 249 

XIV.   INSPECTION    OF    BRICK    AND    BLOCK    PAVEMENTS 

GENERAL  CHARACTERISTICS: 

291.  Types  of  Pavement 250 

292.  General  Method  of  Construction 251 

DETAILS  OF  CONSTRUCTION  APPLICABLE  TO  ALL  TYPES: 

293.  Foundations 251 

™*       ^      i  •                     r,    J  oeo 

294.  Cushions  or  Beds 252 

295.  Laying  the  Brick  or  Block 254 

296.  Compaction 255 

297.  Joint  Filling 256 

298.  Expansion  Joints 259 

299.  Hillside  Construction 259 

300.  Measurement 259 

VITRIFIED  SHALE  AND  CLAY  BRICK: 

301.  Types  of  Brick 259 

302.  Rattler   Test . . 261 


xx  Index  of  Articles 

ARTICLE  PAGE 

303.  Size  ....................  ......................  U.  uil.  262 

304.  Joints  .....  ...  ..............  .............  &JM>:  I  .«ui»:  262 

305.  Visual  Inspection  ...........................  .........  264 

306.  Sampling  ....................................  ..:.!..  265 

'             '                      '  ' 

SLAG  BLOCK: 

307.  Manufacture 

308.  Properties  ..................  .....  ....  ,*iU.  vHuw/r.-uiT.  266 

STONE  BLOCK: 

309.  Types  of  Block  .....................  .;*>>.  .•j.vumiJMi'i  .  266 

310.  Tests  ..................  ..  .  ..  ----  .  .•>iM>fev»Hir.I.*w«-Mwnnjifl.  267 

311.  Size  ............................  ............  ......  y.  267 

312.  Joints  ......................  .'.  "f\  \1™!*'..  "™V!\  r'.J!'/V!  268 

313.  Visual  Inspection  ................  ''.'/'•Kl'.!77^  .''!";  .  .  ;f.  .".;.'.  268 

"314.   Sampling  ..........................  ..::?.'.;'.  .'/y  .'I1',.1.,.  270 

ASPHALT  BLOCK: 

315.  Manufacture  and  Composition  ......  ........  _.'..'.  .".'  1  270 

316.  Tests  .......................................  'i  ..'..'!;.  271 

317.  Size  ......  ...  ............  .................  :  .  :  .  '.  •J.'(.i:  .  271 

318.  Inspection  and  Sampling  ..............  :./..i  !/•<!.  ....I-  *-.'.»  WTJH  272 

WOOD  BLOCK: 

319.  Manufacture  .................  .  .  :  ......  .  .  .  .^VJ  :.".'!'?{-.  273 

320.  Requirements  .......................................  .  .  274 

321.  Joints:  '..  .>[.  )OAf\  .  .c.i./:/.  .  yl'JJ  JUI  .  .;JU  .  X.OJ'JV  WH^'^J.  275 

322.  Inspection  ....................................  .......  277 

323.  Sampling  ........................  :.  i^™/::^V;  278 

ur,<-                                       .                 ......  .    .    tn-Mn'jVji'l  'io  >/»qvT  .I(."J 

MAINTENANCE: 

324.  Methods  ............................................  280 

325.  Inspection:*.!7.  .;.'/.  .'.'  !  .?  J^H™.-!1?^??????^  .'K!  .4?  '  281 

' 


INSPECTOR'S  EQUIPMENT:  ^j 

326.  Construction  .............  .  .  ^w-i*  -tenfr  ^t-  snivel.     281 

327.  Maintenance  ..........  ...  ................  ««>t«MjqMi«'.).     282 

,  .-.  ........  wiillft  iniol   .Tf?£ 

XV.  INSPECTION  OF  MISCELLANEOUS  WORK  AND 

MATERIALS 
BITUMINOUS  EXPANSION  JOINTS: 

328.  General  Characteristics  .....  .....  .....................      283 

329.  Poured  Joints  .......  ......  ...  .  .  .....................     283 

330.  Prepared  Joints,.  .  ..........  .  ........  .  ..........  .  ----     284 


287 


Index  of  Articles  xxi 

ARTICLE  PAGE 

PAVING  ADJACENT  TO  CAB  TRACKS: 

331.  Materials 285 

332.  Methods 285 

COLD  PATCHING: 

333.  Materials 286 

334.  Methods 286 

PIPE  CULVERTS: 

335.  Clay  and  Concrete 

336.  Metal  Pipes 290 

337.  Joints 292 

. 
CONCRETE  FOR  MISCELLANEOUS  STRUCTURES: 

338.  Classes  of  Concrete 292 

339.  Field  Test  for  Cement 292 

340.  Forms 293 

341.  Waterproofing 294 

IRON  AND  STEEL: 

343.  Structural  Steel 296 

MASONRY: 

344.  Types  of  Masonry 296 

345.  Mortar ...     297 

PRESERVATIVE  COATINGS: 

346.  Paints 297 

347.  Dips 297 

NON-BITUMINOUS  DUST  PREVENTIVES  AND  BINDERS: 

348.  Calcium  Chloride 

349.  Sodium  Silicate 

350.  Waste  Sulphite  Liquor.  ...  299 

XVI.   MEASUREMENTS 

GENERAL  CONSIDERATIONS: 

351.  Purpose  of  Measurements 

352.  Classes  of  Measurements . 

353.  Accuracy  of  Measurements 300 

LINEAR  MEASUREMENTS: 

354.  Length 301 


xxii  Index  of  Articles 

ARTICLE  PAGE 

355.  Width 302 

356.  Thickness ; 302 

357.  Testing  Contour  and  Surface  Irregularities 303 

MEASUREMENTS  OF  AREAS: 

358.  Surface  Areas -. .' 304 

359.  Crown  Sections 305 

360.  End  Section  Areas 309 

MEASUREMENT  OF  VOLUMES: 

361.  Volumes  Computed  from  End  Section  Areas 312 

362.  Volumes  Measured  in  Excavation 313 

363.  Capacity  of  Rectangular  Containers 314 

364.  Contents  of  Wagons  and  Barrows 314 

365.  Capacity  of  Tanks 316 

366.  Volumes  Computed  from  Weight. 319 

MEASUREMENT  OF  WEIGHT: 

367.  Weights  Computed  from  Volume. 320 

368.  Direct  Determination  of  Weight 320 

EQUIVALENT  MEASURES: 

369.  Common  Measures 321 

370.  Weight  of  Water 323 

XVII.  MISCELLANEOUS  FIELD  TESTING  AND 
SAMPLING  EQUIPMENT 

TESTS  OF  MINERAL  AGGREGATES: 

371.  Mechanical  Analysis  and  Grading 324 

372.  Organic  Matter  in  Sand 328 

373.  SiltinSand 328 

374.  Quality  of  Gravel  Pebbles 329 

375.  Weight  per  Cubic  Foot ^rt^^nAriak'ZtoR'H'  329 

376.  Specific  Gravity 330 

377.  Voids 332 

TESTS  OF  BITUMINOUS  MATERIALS: 

378.  Penetration  Test  for  Asphalt  Cements 333 

379.  Float  Test  for  Tars 336 

380.  Pat  Test  for  Sheet  Asphalt  Mixtures 337 

381.  Moisture  in  Wood  Block 339 

382.  Absorption  of  Asphalt  Block 341 

383.  Specific  Gravity 342 

384.  Voids  in  Compressed  Bituminous  Paving  Mixtures 342 


1  Index  of  Articles  xxiii 

ARTICLE  PAGE 
MISCELLANEOUS  EQUIPMENT: 

385.  Sampling 343 

386.  Thermometers 344 

387.  Measurements  and  Visual  Inspection 345 

388.  Selection  of  Equipment 345 

XVIII.   RECORDS  AND  REPORTS 

SAMPLES: 

389.  Identification 346 

390.  General  Information 346 

391.  Location  Where  Used .  . 347 

392.  Test  Reports 348 

PROGRESS  OF  WORK: 

393.  Daily  Records 348 

394.  Weekly  Summaries 348 

395.  Paving  Plant  Operation 349 

QUANTITIES  OF  MATERIAL: 

396.  Material  Received 351 

397.  Material  Used 352 

398.  Checks  on  Quantities 352 

COST  DATA: 

.  399.   Labor    353 

400.  Materials 353 

GENERAL  RECORDS: 

401.  The  Inspectors'  Diary 353 

402.  Deviation  from  Specifications 354 

403.  Special  Instructions  from  the  Engineer 354 

404.  Report  Forms 354 

XIX.  TYPICAL   MATERIAL  REQUIREMENTS 

NON-BITUMINOUS  MATERIALS  : 

405.  Broken  Stone 357 

406.  Gravel 358 

407.  Sand 359 

BITUMINOUS  MATERIALS: 

408.  Oil  and  Asphalt  Products  for  Surface  Treatment 359 

409.  Tar  Products  for  Surface  Treatment  and  Cold  Patching. .  360 


xxiv  Index  of  Articles 

ARTICLE  PAGE 

410.  Asphalt  Emulsion  for  Cold  Patching 360 

411.  Refined  Tars  for  Bituminous  Macadam  or  One  Size  Stone 

Bituminous    Concrete .• ,. 360 

412.  Asphalt  Cements  for  Construction ...,......,,...,,,......  361 

413.  Tar  Pitch  for  Grout  for  Joint  Filler , t f  , ,. . . .,.;. < . .... . . .  362 

414.  Creosoting  Oils 362 


iljii/'K  I 
I<:i--vn^v 
,V;ono':I 


JAIIEITAM   .U.:)icIYT   .XIX. 


- 


INDEX   OF   ILLUSTRATIONS 

FIG.  PAGE 

1.  Resistance  of  Rock  to  Abrasion  or  Wear 21 

2.  Toughness  of  Rock 22 

3.  Relation  of  Hardness  to  Toughness 22 

4.  Weight  of  Broken  Stone 28 

5.  Volume  of  Broken  Stone 29 

6.  Weight  and  Volume  Relations  for  Dry  Quartz  Sand ....  39 

7.  Weight  and  Volume  Relations  for  Bituminous  Materials . .  73 

8.  Weight  of  Bitumen  per  Gallon  of  Bituminous  Material ....  74 

9.  Volume  of  Bitumen  per  Ton  of  Asphalt 75 

10.  Volume  of  Bitumen  per  Ton  of  Tar 76 

11.  Volumes,  at  Elevated  Temperatures,   Equivalent  to  100 

Gallons  at  Normal  Temperature 78 

12.  Volumes,    at    Normal    Temperature,    Equivalent   to    100 

Gallons  at  Elevated  Temperature 79 

13.  Equivalents  of  Fahrenheit  and  Centigrade  Scales 88 

14.  Specific  Gravity  Equivalents  for  Baume  Scale  for  Liquids 

Lighter  than  Water 90 

15.  Quantities  of  Material  Required  for  Sand-Clay  Construc- 

tion  '108 

16.  Cubic  Yards  of  Gravel  Required  for  Gravel  Road  Con- 

struction   114 

17.  Tons  of  Gravel  Required  for  Gravel  Road  Construction  ...  115 

18.  Bushels  of  Clean  Oyster  Shells  Required  for  Shell  Road 

Construction 118 

19.  Quantity  of  Broken  Stone  Required  for  Macadam  Con- 

struction   132 

20.  Quantity  of  Broken  Slag  Required  for  Macadam  Con- 

struction   133 

21.  Quantity  of  Materials  Required  for  Bituminous  Surface 

Treatment 147 

22.  Length  of  Road  Which  May  be  Treated  with  100  Gallons 

of  Bituminous  Material 148 

23.  Quantities  of  Materials  Required  for  Bituminous  Macadam 

Construction 160 

24.  Coarse  Aggregate  Required  for  Concrete  Construction ....  181 

25.  Fine  Aggregate  and  Cement  Required  for  Concrete  Con- 

struction   182 

26.  Example  of  Fluxing  Curve 198 

27.  Quantities  of  Materials  Required  for  Construction  of  One- 

size  Stone  Bituminous  Concrete 223 


xxv i  Index   of  Illustrations 

FIG.  PAGE 

28.  Quantities    of    Materials    Required    for    Construction    of 

Coarse  Graded  Aggregate  Bituminous  Concrete 229 

29.  Quantities  of  Material  Required  for  Construction  of  Fine 

Graded  Aggregate  Bituminous  Concrete,  Topeka  Type  234 

30.  Quantities  of  Trinidad  A.  C.  and  Filler  Required  for  Con- 

struction of  Fine  Graded  Aggregate  Bituminous  Con- 
crete, Topeka  Type 235 

31.  Quantities    of   Materials  Required    for   Construction    of 

Binder  Course 238 

32.  Quantity  of  Trinidad  A.  C.  Required  for  Construction  of 

Binder  Course 239 

33.  Quantities  of  Materials  Required  for  Construction  of  Sheet 

Asphalt  Surface  Course 241 

34.  Quantities  of  Trinidad  A.  C.  and  Filler  Required  for  Con- 

struction of  Sheet  Asphalt  Surface  Course 242 

35.  Quantities    of    Materials    Required    for    Construction    of 

Cushions , 253 

36.  Quantities  of  Materials  Required  for  Filling  Joints  in  Brick 

Pavements 263 

37.  Quantities  of  Materials  Required  for  Filling  Joints  in  Stone 

Block  Pavements 269 

38.  Quantities  of  Materials  Required  for  Filling  Joints  in  Wood 

Block  Pavements 276 

39.  Area  of  100  Linear  Feet  of  Road 304 

40.  Length  of  Road  Represented  by  100  Square  Yards 306 

41.  Length  of  Road  Represented  by  1  Square  Yard 307 

42.  Crown  Section  Area 308 

43.  Typical  End  Sections ""  ' '." 309 

44a.  Areas  of  End  Sections  of  Uniform  Thickness 310 

446.  Areas  of  End  Sections  of  Uniform  Thickness 311 

45.  Volumes  per  Linear  Foot  Represented  by  Various  End 

Section  Areas 313 

46.  Example  of  Volume  Contents  of  Loaded  Wagon 315 

47.  Factor  F\t  for  Calculating  Contents  of  Cylindrical  Tanks  . .  317 

48.  Factor  F2,  for  Calculating  Contents  of  Cylindrical  Tanks  . .  318 

49.  Equivalents  of  Inches  in  Decimal  Parts  of  a  Foot . . 322 

50.  Field  Outfit  for  Mechanical  Analysis 325 

51.  Collapsible  Cubic  Foot    Measure 330 

52.  New  York  Testing  Laboratory  Miniature  Penetrometer 334 

53.  New  York  Testing  Laboratory  Float  Apparatus 337 

54.  Pat  Stains 338 

55.  Apparatus  for  Determining  Moisture  in  Creosoted  Wood 

Block.  .  340 


HIGHWAY   INSPECTORS' 
HANDBOOK 


A7/I1«)!II 


HIGHWAY   INSPECTORS' 
HANDBOOK 

CHAPTER  I 
HIGHWAY  INSPECTION 

THE  INSPECTOR 

1.  Highway   Inspection.     Webster   defines   inspection   as 
a  careful  viewing  or  examining  to  ascertain  quality  or  con- 
dition," and  an  inspector  as  "one  to  whose  care  the  execu- 
tion of  any  work  is  committed,  for  the  purpose  of  seeing 
it  faithfully  performed."    Faithful  performance  presupposes 
work  done  in  accordance  with  a  definite  understanding  or 
under  stipulated  conditions.     In  highway  work  the  stipu- 
lated conditions  are  usually  covered  by  written  or  printed 
specifications  which  should  always  be  incorporated  in  the 
contract  if  the  work  is  done  under  contract.     The  highway 
Inspector  should,  therefore,  possess  and  carry  with  him  for 
reference  a  copy  of  the  specifications  covering  work  which 
he  is  inspecting.     His  first  duty  is  to  ascertain  whether  or 
not  the  conditions  of  the  specifications  are  being  fulfilled 
at  all  stages  of  the  work. 

2.  Qualification  of  Inspectors.     An  inspector  should  first 
of  all  possess  sufficient  knowledge  of  the  work  which  he 
inspects  to  thoroughly  understand  the  requirements  of  the 
specifications   covering  the  work.     This  frequently  neces- 
sitates a  certain  amount  of  experience.     No  matter  how 

1 


2  Highway  Inspection 

intelligent .  he  iaay  be,  a  perfectly  green  man  will  seldom 
make  a  good  inspector.  t  Before  being  placed  in  charge  of 
important .  inspection  he  should,  therefore,  have  acquired 
some  experience  in  highway  work  under  a  competent  in- 
spector. He  should  possess  good  judgment  and  tact  and 
should  be  keenly  observant,  as  the  slighting  of  apparently 
minor  details  of  the  work  may  result  in  unsatisfactory  con- 
ditions which  cannot  be  easily  remedied.  He  should  be 
conscientious,  loyal,  and  capable  of  standing  up  for  what 
he  believes  to  be  right  in  the  face  of  persuasion  or  opposi- 
tion. He  should  have  a  well  balanced  understanding  of  his 
authority  and  the  limits  of  his  authority  and  should  fully 
appreciate  his  responsibilities. 

3.  Responsibility  of  Inspectors.  While  the  Engineer  is 
in  responsible  charge  of  the  work  it  is  impracticable  for  him 
to  be  on  the  job  at  all  times.  He  is,  therefore,  obliged  to 
delegate  a  portion  of  his  responsibility,  that  of  detailed 
observation,  to  the  Inspector.  The  Inspector,  then,  first  of 
all,  serves  as  the  eyes  of  the  Engineer  for  features  of  the 
work  to  which  the  Engineer  is  unable  to  devote  his  continual 
attention.  It  is  practically  impossible  from  the  visual  ex- 
amination of  newly  completed  work  to  ascertain  whether  or 
not  such  work  has  been  done  in  the  satisfactory  manner, 
and  with  the  satisfactory  materials  presumably  covered  by 
the  specifications.  The  work  upon  its  face  may  appear 
satisfactory  and  ultimately  show  defects  which  conclusively 
prove  that  it  could  not  have  been  done  in  accordance  with 
specifications.  At  such  times  it  may  be  too  late  to  hold 
the  Contractor  responsible.  Noting  all  evidences  of  un- 
satisfactory workmanship  and  materials  which  he  has  ob- 
served and  which  have  not  been  corrected  by  the  Contractor 
is  the  principal  responsibility  of  the  Inspector.  In  case  it 
should  develop  that  the  specifications  are  faulty  in  any 
respect  this  fact  should  also  be  noted  so  that  if  desired  a 
satisfactory  adjustment  may  be  made  between  the  Engi- 
neer and  the  Contractor.  There  are  three  general  classes 


Classes  of  Inspection  3 

of  inspection,  one  or  more  of  which  are  necessary  in  road 
and  paving  work.  These  are  laboratory  inspection,  plant 
inspection,  and  roadside  inspection. 

CLASSES  OF  INSPECTION 

4.  Laboratory     Inspection.     Laboratory     inspection     is 
largely  confined  to  the  examination  or  testing  of  road  ma- 
terials for  the  purpose  of  ascertaining  whether  or  not  they 
conform  with  specifications.     In  certain  instances  it  may 
also  serve  to  indicate  whether  methods  of  work  have  been 
carried   out   in   accordance   with   specifications,    as   in   the 
examination  of  a  sample  of  bituminous  concrete,  or  a  sec- 
tion of  the  completed  highway.     The  laboratory  Inspector 
may  be  called  upon  to  conduct  both  involved  chemical  and 
physical  tests  and,  for  this  reason,  may  properly  be  a  trained 
chemist,  testing  engineer  or  chemical  engineer.    He  may,  to 
some  extent,  deal  directly  with  the  Engineer,  plant  Inspec- 
tor  or  roadside   Inspector.     His   duties  are  more   or  less 
specialized,  and  except  as  they  relate  to  other  classes  of 
inspection,  will  not  be  considered  in  this  handbook. 

5.  Plant  Inspection.     Plant  inspection  has  to   do  with 
plant   sampling   and   testing   of   road   materials,    measure- 
ments of  quantities  and  often  control  of  proportions  of  ma- 
terials,   temperature    observations,    and    the   inspection    of 
such  portions  of  the  plant  methods  of  operation  and  proce- 
dure as  may  be  covered  by  specifications  or  may  materially 
affect  the  character  and  quality  of  the  work.    Plant  inspec- 
tion of  materials  is  usually  limited  to  visual  inspection  and 
a  few  simple  physical  tests,  which  check  or  are  eventually 
checked  by  the  laboratory.     Irrespective  of  the  character  of 
work  performed,  there  are  four  functions  of  a  plant,  one  or 
more  of  which  may  require  inspection.     These  are  receiv- 
ing,  storing,   preparing  and   distributing  or  shipping  ma- 
terials.    There  are  two  classes  of  plants,  those  in  which 
certain  individual  constituents  of  a  road  or  pavement  are 


4  Highway  Inspection 

prepared  or  handled,  and  those  in  which  the  paving  material 
proper  is  prepared.  As  an  example  of  the  former  may  be 
mentioned  petroleum,  asphalt  or  tar  refineries  where  bi- 
tuminous road  materials  are  manufactured.  When  condi- 
tions warrant,  an  inspector  may  be  placed  at  such  a  refinery 
to  sample  the  manufactured  product,  observe  its  storage, 
seal,  open  and  reseal  storage  tanks,  measure  .quantities, 
mark  or  stamp  containers,  watch  the  loading  of  shipments 
of  approved  materials,  and  seal  cars  or  containers.  Among 
plants  of  the  class  which  prepare  or  handle  the  paving 
material  proper  may  be  mentioned  bituminous  concrete  or 
sheet  asphalt  paving  plants,  asphalt  block  plants,  and  creo- 
soting  plants  engaged  in  the  manufacture  of  creosoted  wood 
paving  blocks.  At  such  plants  the  Inspector  may  sample 
and  test  not  only  the  individual  constituents  of  the  pave- 
ment, but  also  the  prepared  paving  composition  and,  in 
addition,  observe  and  record  certain  details  of  its  prepara- 
tion. This  is  the  most  common  class  of  plant  inspection 
and  is  covered  in.  detail  in  subsequent  chapters. 

6.  Roadside  Inspection.  Roadside  inspection  covers 
either  the  field  sampling  and  visual  examination  of  the  indi- 
vidual constituents  of  the  road  or  pavement,  or  of  the  pav- 
ing material  proper,  measurements  of  quantities  and  dis- 
tribution of  such  materials  as  are  received  and  placed  upon 
the  road,  frequently  temperature  observations,  and  the 
inspection  of  such  details  of  work  as  are  included  in  the 
specifications  or  may  be  necessary  to  produce  a  satisfactory 
job.  In  some  instances  the  paving  material  may  be  pre- 
pared at  the  site  of  work  or  at  roadside  plants.  Where 
this  is  the  case,  the  Inspector  may  have  to  assume  the 
responsibility  of  both  plant  and  roadside  inspection.  It 
frequently  happens,  however,  that  the  plant  may  be  located 
at  a  considerable  distance  from  the  work  and  that  the 
services  of  at  least  two  inspectors  will  be  required  to  see 
that  the  work  is  faithfully  performed  in  accordance  with 
specifications.  When  this  is  so  the  two  Inspectors  should 


Relations  of  the  Highway  Inspector          5 

. 

in  harmony  and  keep  in  close  touch  with  one  another. 
I  Both  plant  and  roadside  inspectors  may  have  occasion  to 
;  submit  samples  of  materials  to -the  laboratory  for  examina- 
i  bion  as  directed  by  the  Engineer  or  requested  by  the  Labora- 
tory.    They  may  also  submit  samples  on  their  own  initia- 
tive when  they  have  reason  to  suspect  that  any  material 
fails   to   conform   with   specifications,   but   do   not   possess 
[adequate  facilities  for   ascertaining  whether  or   not   their 
i  suspicions  are  well  founded.    Either  may  at  times  >e  called 
;upon  to  sample  and  inspect  natural  deposits  of  material 
i  such  as  sand,  gravel  or  rock.    In  addition  to  the  inspection 
above  described  the  Inspector  may  be  called  upon  to  examine 
and  report  upon  the  condition  of  a  road  or  pavement  any 
time  after  its  completion.     In  some  respects  this  is  the 
highest  class  of  inspection,  as  the  Inspector  then  has  but 
little  to  guide  him  in  his  work  and  must  depend  to  a  large 
extent  upon  his  natural  powers  of  observation  and  deduc- 
tion,  supplemented   by  his  experience  and   possibly  by  a 
laboratory   examination   of   sections   of  the   pavement   re- 
moved under  his  direction. 

RELATIONS   OF  THE  HIGHWAY  INSPECTOR 

7.  The  Engineer.  The  Inspector  comes  immediately 
under  the  authority  of  the  Engineer  and  should  take  in- 
structions from  no  one  else  unless  so  directed  by  the  engi- 
neer. He  should  carry  out  the  Engineer's  instructions 
explicitly  and  give  his  loyal  support  to  the  observance  of 
his  directions,  both  as  furnished  by  the  specifications  and 
as  stated  verbally.  On  the  other  hand,  the  Engineer  should 
afford  loyal  support  to  his  inspector  if  the  latter  keeps  within 
the  limits  of  his  authority  and  exercises  good  judgment.  In 
case  of  misunderstandings  or  errors  on  the  part  of  the  in- 
spector, the  Engineer  should  never  reprimand  him  before 
the  Contractor,  foreman,  or  any  of  the  working  force.  He 
should  first  of  all  see  that  his  specifications  are  not  only  so 


Highway  Inspection 


explicit  that  misunderstandings  are  practically  eliminated, 
but  he  should  also  take  precautions  that  they  are  techni- 
cally correct  so  that  no  legitimate  error  will  result  in  either 
the  inspection  or  execution  of  the  work.  Unless  the  rela- 
tions between  the  Inspector  and  Engineer  are  of  long  stand- 
ing so  that  both  are  thoroughly  familiar  with  each  other's 
methods,  the  Engineer  should  invariably  instruct  the  In- 
spector as  to  his  limits  of  authority  for  each  contract  and 
furnish  him  with  advance  detailed  directions  regarding  the 
conduct  of  his  work  if  such  directions  are  necessary.  Finally 
the  Inspector  should  be  under  the  control  of  the  Engineer 
to  the  same  extent  in  public  service  work  as  in  private 
engineering  practice. 

8.  The  Laboratory.  The  laboratory  is  a  necessary  ad- 
junct to  road  and  paving  work,  and,  under  the  direction  of 
the  Engineer,  may  deal  directly  with  the  Inspector  with 
regard  to  certain  matters.  In  some  cases,  as  for  instance 
a  bituminous  concrete  paving  plant,  the  Inspector  may 
himself  conduct  certain  laboratory  tests,  but  he  should 
always  rely  upon  a  well-equipped  chemical  or  testing  labo- 
ratory to  furnish  the  detailed  examination  of  the  materials 
which  he  inspects.  In  addition  to  this  the  control  labora- 
tory serves  as  a  check  upon  the  field  tests  made  by  the 
Inspector.  The  relations  between  the  Laboratory  and  the 
Inspector  should  be  clearly  defined  to  each  by  the  Engi- 
neer. Usually  the  Inspector  samples  all  shipments  of 
materials  received  and  forwards  them  direct  to  the  Labora- 
tory, whose  report  of  examination  and  acceptance  he  should 
obtain  prior  to  their  use  in  the  work.  In  addition,  through- 
out the  work  he  may  be  required  to  send  to  the  Laboratory 
check  samples  of  materials  which  he  tests  and  should  keep 
himself  informed  as  to  how  his  own  results  compare  with 
those  of  the  Laboratory.  He  may  at  various  times  bei 
requested  by  the  Laboratory  to  submit  special  samples  and 
if  during  the  course  of  the  work  he  has  any  reason  to  sus-  \ 
pect  the  character  of  material  which  has  already  been| 


Relations  of  the  Highway  Inspector          7 

sampled  and  tested  he  should  submit  a  new  sample  of  such 
material.  In  case  the  Laboratory  examination  shows  slight 
variations  of  a  material  from  specification  requirements  the 
Laboratory  should  indicate  upon  its  report  to  the  Inspector 
whether  or  not  the  material  will  be  accepted  and,  if  so, 
with  or  without  warning  to  the  contractor.  Such  matters 
should,  of  course,  be  decided  by  the  Engineer,  who  may 
prefer  to  personally  communicate  with  the  Inspector  after 
conferring  with  the  Laboratory. 

9.  The  Contractor,  (a)  While  the  first  duty  of  the 
Inspector  is  to  see  that  the  Contractor  performs  his  work 
faithfully  in  accordance  with  the  specifications,  it  is  of  the 
utmost  importance  for  him  to  exercise  good  judgment  and 
tact  in  his  relations  with  the  Contractor.  To  this  end  he 
should  endeavor  to  delay  or  hinder  the  operations  of  the 
Contractor  as  little  as  possible,  and  should  inspect  materials 
promptly.  He  should  never  accept  extraordinary  favors 
from,  nor  obligate  himself  to  the  Contractor  in  any  manner. 
On  the  other  hand  he  should  never  allow  the  Contractor 
to  work  a  modification  or  substitution  of  any  details  of 
the  specifications  unless  such  change  has  been  made  known 
to  and  first  approved  by  the  Engineer.  The  limit  of  his 
authority  as  related  to  the  Contractor  should  be  clearly 
defined  by  the  Engineer  both  to  him  and  to  the  Contractor 
so  that  there  may  be  no  conflict  through  misunderstand- 
ings. As  a  rule,  the  Inspector  should  never  give  orders  to 
laborers  on  the  work,  but  should  deal  directly  with  the 
Contractor  or,  in  the  Contractor's  absence,  with  his  fore- 
man. Unless  specifically  authorized  to  do  so  by  the  Engi- 
neer he  should  not  actually  direct  the  Contractor,  but  should 
immediately  notify  him  of  any  and  all  violations  of  the 
specifications.  If  the  violation  is  not  vital  the  work  or 
material  may  be  accepted  with  warning  that  further  viola- 
tion will  cause  rejection.  In  case  of  dispute  as  to  the  inter- 
pretation of  specifications  the  matter  should  be  immediately 
taken  to  the  Engineer  for  decision. 


8  Highway  Inspection 

(6)  While  the  specifications  should  be  technically  correct 
and  readily  understandable,  such  is  not  always  the  case.  It 
is,  therefore,  often  good  policy  for  the  Engineer,  Inspector 
and  Contractor  to  hold  a  conference  preceding  the  actual 
work  and  to  review  each  requirement  of  the  specifications 
until  a  common  understanding  is  reached.  Work  should 
be  suspended  by  direction  of  the  Inspector  only  under  con- 
ditions to  be  prescribed  by  the  Engineer.  The  Inspector 
should  keep  a  detailed  diary  of  his  observations  throughout 
the  work,  noting  particularly  all  warnings  and  instructions 
given  to  the  Contractor.  There  are,  of  course,  all  classes 
of  contractors  from  those  who  are  conscientious  and  honest 
to  those  who  are  unscrupulous  and  dishonest.  Until  known 
to  the  contrary,  however,  it  may  be  assumed  that  the 
Contractor  will  take  pride  in  his  work  and  will  endeavor  to 
give  satisfaction,  particularly  if  he  can  at  the  same  time 
make  a  fair  and  reasonable  profit.  Natural  dishonesty 
cannot  well  be  eliminated  except  by  experience  and  refusal 
to  let  a  contract  to  any  contractor  who  has  already  proved 
dishonest.  It  is  exceedingly  difficult  to  secure  good  work 
if  it  is  not  profitable  to  the  Contractor.  A  contract  should 
only  be  let  when  prospects  of  a  reasonable  profit  are  assured. 
Even  then,  however,  the  foreman,  through  a  natural  desire 
to  cut  expenses  for  his  employer,  may  resort  to  evasion  of 
specification  requirements,  the  importance  of  which  he  does 
not  appreciate,  and  efficient  inspection  will  be  required  to 
secure  a  satisfactory  job. 

SPECIFICATIONS 

10.  General  Scope  of  Specifications.  In  addition  to 
other  sections  specifications  are  frequently  printed  under 
such  headings  as  Definition  of  Terms,  General  Provisions, 
Construction  Details,  and  Material  Requirements.  Under 
one  of  these  headings,  usually  ''General  Provisions,"  certain 
stipulations,  commonly  made,  are  dealt  with  in  the  follow- 


Specifications 


ing  paragraphs.  If  these  details  are  lacking  the  Inspector 
should  request  specific  instruction  from  the  Engineer  regard- 
ing all  which  may  be  of  importance  in  the  work  to  which 
he  is  assigned. 

11.  Basis  of  Measurement  and  Payment.     In  a  given 
contract  payment  is,  of. course,  made  both  for  work  per- 
formed and  materials  furnished.     The  basis  for  measure- 
ment, however,  may  vary.     Some  items  may  require  bids 
on  the   quantity  of  acceptable  material  delivered   on  the 
work  and  other  items  may  be  on  the  quantity  of  work  and 
material  in  place.    In  either  case  it  should  be  made  possible 
for   the    Inspector   to    check   quantities   with    considerable 
accuracy.     For  materials  delivered  on  the  job,  bills  of  lad- 
ing, measurements  of  the  capacity  of  containers  and  direct 
weights  may  all  be  utilized.     For  work  in  place,  measure- 
ments of  surface  and  depth  or  of  volume  may  be  made. 
If  surface  measure  is  to  be  used  the  method  of  taking  such 
measurement    should    be    clearly    stated    and    understood. 
Thus  it  may  be  specified  that  as  a  basis  for  payment  the 
surface  of  a  roadway  shall  be  measured  horizontally  (§358). 
In  the  case  of  heavy  grades  this  method  may  show  materially 
less  yardage  than  though  the  actual  surface  of  the  road  was 
measured,  as  the  horizontal  length  of  the  road  shown  on 
the  plans  then  represents  the  base  of  a  triangle  while  the 
actual   length   is   its   hypotenuse.      The   following   stipula- 
tion  is    cited    as    an    example    of    an    ordinarily    satisfac- 
tory   basis    of    measurement.      "All    linear    surface    meas- 
urements  of    work   done   will   be   made   along   the   center 
line  of  actual  surface  of  the  roadway  and  not  horizontally, 
and  the  area  paid  for  shall  be  only  the  actual  area  covered 
by  the  entire  surfacing  or  paving  material  wthin  the  lines 
designated  or  given,  except  that  no  deduction  will  be  made 
for  fixtures  in  the  roadway  or  street  with  an  area  of  9  square 

feet  or  less." 

12.  Cooperation  of  Contractor  on  Inspection.     In  order 
-  that  the  Inspector  may  not  be  hampered  in  the  performance 


10  Highway  Inspection 

of  his  duties,  specifications  should  provide  that  if  requested, 
the  Contractor  shall  furnish  the  Engineer  or  his  representa- 
tive with  bills  of  lading  or  correct  copies  thereof  of  shipments 
of  all  materials  used  and  shall  furnish  every  reasonable 
facility  for  ascertaining  the  quantity  of  material  received 
and  used  as  well  as  its  source.  It. should  also  be  stipulated 
that  when  practicable  stored  materials  shall  be  so  located 
as  to  facilitate  prompt  inspection,  and  that  when  tests  are 
made  at  places  other  than  the  Laboratory  the  Contractor 
shall  furnish  every  facility  necessary  for  the  verification  of 
all  scales,  measures  and  other  devices  which  he  operates. 

13.  Inspection  Details.     Specifications  should  inform  the 
Contractor  that  all  materials  proposed  to  be  used  may  be 
inspected  at  any  time  during  the  progress  of  their  prepara- 
tion and  use.    They  should  also  state  that  if  after  trial  it  is 
found  that  sources  of  supply,  which  have  been  approved 
upon  samples  previously  examined,  do  not  furnish  a  product 
within  the  specification  requirements,  the  Contractor  shall 
furnish  approved  material  from  another  source.     In  addi- 
tion it  should  be  stipulated  that  after  approval,  any  material 
which  has  become  mixed  with  or.  coated  by  dirt  or  other 
foreign  material  shall  not  be  used  on  the  work,  and  that  all 
rejected  material  shall  be  promptly  removed  from  the  site 
of  work. 

14.  Removal  and  Replacement  of  Work.     Inspection  of 
completed  work  in  which  it  is  deemed  necessary  to  cut  out 
or  remove  sections  of  the  pavement  should  be  specifically 
cared  for  in  the  specifications  so  that  there  will  be  no  mis- 
apprehension on  the  part  of  the  Contractor  with  consequent 
dispute.     It  should  be  stipulated  that  if  the  Engineer  re- 
quests it,  the  Contractor,  at  any  time  before  acceptance 
of  the  work,  shall  remove  or  uncover  such  portions  as  may 
be  directed,  and  that  after  examination  the  Contractor  shall 
restore  such  portions  of  the  work  to  the  standard  required 
by  the  specifications.     Should  the  work  thus  exposed  or 
examined   prove   acceptable,   the  uncovering  or  removing 


Specifications  11 

and  replacing  should  be  paid  for  as  extra  work  on  a  basis 
clearly  stated  in  the  specifications,  but  should  the  work  so 
exposed  or  examined  prove  unacceptable,  the  uncovering 
or  removing  and  the  replacing  or  making  good  of  the  parts 
removed  should  be  at  the  Contractor's  expense. 


CHAPTER  II 
BROKEN  STONE 

ROCK 

15.  Occurrence.     Rock  occurs  most  commonly  in  mas- 
sive formation  such  as  ledges  or  beds  of  interlocking  mineral 
constituents  of  a  crystalline  nature.     Certain  deposits  are, 
however,   of  an  amorphous    or    noncrystalline  nature  and 
possess  a  smooth  or  glassy  texture.     Rock  also  occurs  as 
field  stone  in  the  form  of  bowlders  which  have  usually  been 
transported   and   deposited   by   glacial   action.      Individual 
rock  deposits  are  not  always  uniform  in  composition,  appear- 
ance or  physical  properties,  and  this  fact  should  be  borne 
in  mind  by  the  Inspector,  particularly  when   a  source  of 
supply  has  been  approved  or  is  subject  to  approval  upon 
the  results  of  tests  of  samples  submitted.     Strata  or  dikes 
of  different  rock  families  may  even  occur  in  the  same  deposit. 
Numerous  varieties  of  rock  are  found  in  certain  sections  of 
the  country  while  other  sections  are  either  devoid  of  rock 
or  contain  a  limited  number  of  varieties.    As  it  is  the  most 
extensively  used  of  all  road  materials  and  its  transporta- 
tion is  expensive,  local  occurrence  largely  governs  specifica- 
tions for  characteristics   of  rock  to   be   used  in  highway 
construction. 

16.  Classification.     Rocks  are  most  accurately  classified 
according  to  origin,   method   of  formation,   structure  and 
mineral  composition.     There  are  three  general   classes  of 
road-building  rock  which  are  subdivided  into    types    and 
families  as  shown  in  the  following  Table:* 

*  E.  C.  E.  Lord,  U.S.  Dept.  Agri.  Bui.  No.  348. 
12 


Rock 


13 


GENERAL  CLASSIFICATION  OF  ROCKS 


Class 

Type 

1.  Intrusive    (plutonic) 

[a.  C 
b.  S 
c.   I 
d.  C 

I.    Igneous ! 


II.    Sedimentary 
or  Aqueous 


III.   Metamorphic 


2.  Extrusive  (volcanic) 
1.  Calcareous  .  . 


2.  Siliceous../ 


1.  Foliated. . 


2.  Nonfoliated. 


Family 


e.  Peridotite. 

a.  Rhyolite. 

b.  Trachyte. 

c.  Andesite. 

d.  Basalt  and  diabase. 

a.  Limestone. 

b.  Dolomite. 

a.  Shale. 

b.  Sandstone. 

c.  Chert  (flint). 

a.  Gneiss. 

b.  Schist. 

c.  Amphibolite. 

a.  Slate. 

b.  Quartzite. 

c.  Eclogite. 

d.  Marble. 


Igneous  rocks  have  been  formed  either  below  or  at  the 
surface  of  the  earth  by  crystallization  or  solidification  from 
a  molten  condition.  Sedimentary  or  aqueous  rocks  have 
been  formed  by  water  deposition  and  compression.  Meta- 
morphic rocks  have  been  formed  from  either  igneous  or 
sedimentary  rocks  through  pressure,  heat  or  chemical  action 
which  results  in  an  alteration  of  the  original  rock  structure 
or  mineral  composition.  Alternation  in  structure,  to  the 
extent  of  producing  cleavage  planes,  which  can  usually  be 
distinguished  by  visual  inspection,  produces  the  foliated 
type.  For  ordinary  purposes  the  Inspector  may  consider 
road-building  rock  under  the  following  five  groups,  without 
reference  to  all  of  the  families  shown  in  the  Table: 


14  Broken  Stone 

(a)  Trap    Rock    (including    Andesite,    Basalt,    Diabase, 

Diorite,  Gabbro  and  Rhyolite). 
(6)  Granite  and  Gneiss. 

(c)  Limestone     (including     Limestone,     Dolomite     and 

Marble) . 

(d)  Sandstone  and  Quartzite. 

(e)  Chert. 

Schist,  shale  and  slate  are  highly  laminated  rocks  that  tend 
to  break  into  flat  plates  not  suitable  for  road-building  pur- 
poses, except  sometimes  as  a  filling  for  sub-base  or  founda- 
tion. The  other  families  not  covered  in  the  five  groups 
enumerated  are  rare  from  the  standpoint  of  highway  work. 

17.  Manufacture  of  Broken  Stone,  (a)  Before  rock  is 
suitable  for  use  in  highway  work  it  must  be  reduced  to 
fragments  of  proper  size.  Except  in  the  case  of  field  stones 
this  first  involves  quarrying.  There  are  two  general  types 
of  quarries,  —  the  permanent,  which  is  usually  a  commer- 
cial quarry,  the  general  character  of  product  being  well 
known,  and  the  temporary  quarry  which  is  often  opened 
and  worked  by  the  Contractor  to  supply  work  for  a  single 
contract.  In  the  latter  cases  the  highway  inspector  may 
be  required  to  sample  the  deposit  before  the  quarry  is 
opened  (§  39).  After  the  rock  is  blasted  and  mauled  or 
broken  to  proper  size,  it  is  passed  through  a  crusher,  where 
it  is  further  reduced,  after  which  it  is  screened  into  various 
grades  or  sizes  demanded  by  the  trade. 

(6)  The  most  important  part  of  the  equipment  of  the 
crushing  plant,  insofar  as  size  or  grading  of  the  output  is 
concerned,  is  the  screen.  Various  types  of  screens  and 
methods  of  screening  are  used,  all  of  which  together  with 
the  type  and  setting  of  the  crusher  influence  the  quantity 
and  grading  of  the  various  size  products  manufactured. 
The  most  common  type  is  the  single  revolving  screen  com- 
posed of  four  connected  cylindrical  metal  sections,  each 
section  carrying  circular  perforations  of  a  different  diameter 


Physical  Properties  15 

from  those  of  other  sections.  A  dust  jacket  or  section  of 
shorter  length  but  larger  diameter,  with  small  perforations 
or  mesh  openings,  is  frequently  placed  around  the  regular 
section  containing  the  smallest  perforations.  Broken  stone 
from  the  crusher  is  passed  into  this  end  of  the  revolving 
screen  and  fragments  too  large  to  pass  the  largest  perfora- 
tions are  discharged  from  the  other  end  to  be  recrushed. 
The  product  passing  each  section  is  discharged  by  suitable 
means  into  bins  provided  for  the  various  sizes.  Another 
type  of  revolving  screen  is  composed  of  a  set  of  two  or  more 
concentric  cylindrical  sections  carrying  perforations  of 
different  diameter.  Bar  or  grid,  and  shaking  or  pulsating 
screens  are  less  commonly  used.  In  large  quarries  batteries 
of  screens  may  be  employed,  sometimes  with  small  crushers 
placed  between  to  crush  the  tailings  before  they  are  passed 
over  the  next  screen. 

(c)  Because  a  commercial  broken-stone  product  has 
passed  a  screen  with  a  given  size  opening  and  has  been 
retained  on  a  screen  with  a  smaller  known  opening,  it  does 
not  follow  that  the  grading  or  even  the  average  size  of  the 
product  is  at  all  constant.  There  are  many  other  factors 
which  may  cause  great  variation  in  grading  and  average 
size,  such  as  character  of  the  rock,  setting  of  crusher,  moist 
or  dry  condition  of  the  crusher  output,  rate  of  feeding  into 
the  screen,  inclination  and  rate  of  revolution  of  the  screen, 
and  the  length  of  its  sections.  These  facts  must  be  borne 
in  mind  by  the  Inspector  when  determining  whether  or 
not  a  product  meets  specification  requirements  for  size  (§  18). 

PHYSICAL  PROPERTIES 

18.  Specification  Requirements,  (a)  Specifications*  for 
broken  stone  may  require  a  given  group  or  rock  family  to 
be  used,  or  may  eliminate  by  name  certain  kinds  of  rock 
and  allow  all  others  which  possess  satisfactory  physical 
characteristics.  They  frequently  eliminate  weathered  or 


16  Broken  Stone 

disintegrated  stone.  It  is  therefore  advisable  for  the  In- 
spector to  be  able  to  identify  the  most  important  groups 
by  visual  inspection  or  simple  field  test.  In  addition, 
specifications  may  eliminate  certain  kinds  of  rock  or  cer- 
tain products  by  requiring  that  they  be  free  from  thin  or 
elongated  pieces. 

(b)  Physical  properties  most  commonly  covered  by  speci- 
fications  are  resistance   to   abrasion,   usually  expressed   as 
maximum  per  cent  of  wear  or  minimum  French  coefficient 
of  wear,  and  minimum  toughness.     A  minimum  hardness 
coefficient    and  a  minimum  cementing  value  are  less  fre- 
quently specified.     Determinations  of  these  values  are  a 
matter  of  laboratory  test  which  the  Inspector  is  not  ex- 
pected to  make. 

(c)  The  size  or  grading  of   broken-stone    products  may 
be  specified  in  a  number  of  ways  only  one  of  which,  however, 
that  based  upon  the  results  of  screen  tests,  constitutes  an 
accurate  description.     A  certain  commercial  grade  such  as 
No.  3  may  be  required;    the  allowable  maximum  or  maxi- 
mum  and   minimum   dimensions   of   individual   fragments 
in  the  product  may  be  stated;  the  size  rings  through  which 
a  product  must  pass  and  be  retained  may  be  given;    or  a 
product  which  actually  passes  a  certain  size  opening  and  is 
retained  on  a  smaller  opening  in  a  commercial  screen  may 
be  specified.     All  such  specifications  are  faulty  in  the  fact 
that  they  do  not  accurately  describe  the  desired  product  or 
else  do  not  make  it  possible  for  the  Inspector  to  intelligently 
pass  upon  its  acceptability.    A  far  better  method  is  to  specify 
a  product  which  will  give  results  within  stated  limits  when 
subjected  to  screen  analysis   or  test  which  the  Inspector 
himself  may  make  (§371). 

19.  Important  Rock-forming  Minerals,  (a)  In  order  to 
identify  the  principal  road-building  rocks  with  some  degree 
of  accuracy,  the  Inspector  should  be  able  to  at  least  dis- 
tinguish between  the  most  common  rock-forming  minerals. 
This  may  often  be  done  with  the  unaided  eye,  although 


Physical  Properties  17 

the  use  of  a  small  magnifying  glass  will  be  found  helpful, 
particularly  in  the  case  of  fine-grained  rock.  Moistening  a 
freshly  broken  rock  surface  will  frequently  aid  in  the  matter 
of  identification. 

(6)  Quartz  is  an  extremely  hard  mineral  occurring  in  the 
rock  sample  in  crystals  of  irregular  or  rounded  shape.  It 
is  identified  by  its  almost  colorless  transparency  and  vitre- 
ous or  glassy  luster.  When  present  in  large  quantities  and 
firmly  held  in  the  rock  structure,  it  imparts  to  the  rock  great 
hardness  and  high  resistance  to  wear. 

(c)  Feldspars,  of  which  there  are  numerous  varieties,  are 
hard  brittle  minerals  occurring  as  tabular  or  lath-shaped 
crystals.  They  exhibit  a  variety  of    color    and    are    char- 
acterized by  perfect  cleavage  along  planes  almost  at  right 
angles  to  each  other.     They  may  usually  be  identified  by 
the  pearly  luster  of  these  cleavage  faces.    Rock  which  con- 
tains large  quantities  of  feldspar  tends  to  break  into  cubical 
fragments.     If  the  feldspar  crystals  are  small,  hardness  and 
toughness  are  imparted  to  the  rock;    if  large,  the  property 
of  toughness  becomes  less. 

(d)  Augite  and  Hornblende  occur  as  elongated  crystals 
running  in  shade  from  green  to  black.     When  present  in 
considerable  amount  they  impart  to  the  rock  a  peculiar 
and   well-defined  interlocking    structure    which    results    in 
high  toughness. 

(e)  Mica,   both  white   (Muscovite)   and  black   (Biotite), 
occurs  in   thin   glistening  plates   or  flakes  which  may  be 
easily  scratched  with  a  knife.     It  possesses  a  highly  lami- 
nated structure  and  when  present  in  large  amounts  is  largely 
responsible  for  the  foliated  structure  of  metamorphic  rocks, 
which  tend  to  break  into  flat  fragments. 

(/)  Rock  glass,  which  occurs  in  certain  igneous  rock,  has 
no  crystalline  form  but  occurs  as  a  dark  vitreous  magma 
filling  interstices  between  the  mineral  crystals.  It  is  very 
brittle  and  when  present  in  appreciable  quantity  tends  to 
lower  the  toughness  of  a  rock. 


18  Broken  Stone 

(0)  Calcite  and  Dolomite  are  relatively  soft  carbonate 
minerals  which  may  readily  be  scratched  with  a  knife.  They 
may  exhibit  a  variety  of  colors  due  to  impurities  but 
usually  run  from-  white  to  dark  gray.  Calcite  may  be 
distinguished  by  its  free  effervescence  when  treated  with 
cold  dilute  hydrochloric  acid,  while  dolomite  effervesces 
only  when  treated  with  the  .concentrated  acid.  They 
usually  impart  cementitiousness  to  rocks  in  which  they 
occur. 

20.  Trap  Rock.     The  name  trap  is  commonly  applied 
to  all  dense,  fine-grained,  igneous  rock  running  from  gray 
to  black  in  color.     These  rocks  invariably  contain  fine  crys- 
tals of  feldspar,  usually  averaging  between  20  and  60   per 
cent  in  volume.    Most  varieties  carry  a  high  percentage  of 
either  augite  or  hornblende,  or  both,  and  sometimes  chlorite, 
a  dark  green  mineral,  is  present  in  considerable  amount. 
Quartz  may  either  be  absent,  or  present  to  the  extent  of 
over   30   per   cent,  and   the   same   is   true   of   rock   glass. 
Mica  is  either  absent,  or  present  in  the  black  variety  to 
only  a  limited  extent.    When  crushed,  trap  tends  to  break 
into  cubical  fragments.     It  usually  possesses  high  tough- 
ness, hardness,  and   resistance   to   abrasion.      It   averages 
close  to  2.9  specific  gravity,  although  individual  samples 
sometimes  run  as  low  as  2.7  and  as  high  as  3.2 

21.  Granite  and  Gneiss.     Granite  and  its  metamorphic 
brother  Gneiss  are  typical  rather  coarse-grained  rocks  com- 
posed essentially  of  quartz  and  feldspar  with  a  less  amount 
of  mica.     Augite  and  hornblende  may  be  absent,  but  the 
latter  is  not  an  uncommon  constituent  of  both.     They  ex- 
hibit a  variety  of  colors,  but  are  usually  gray  or  pink.     The 
fracture  of  granite  is  rough  and  more  rectangular  than  that 
of  trap.     Gneiss  is  distinguished  from  granite  by  its  foliated 
or  stratified  structure  which  tends  to  cause  it  to  break  into 
rather  flat  fragments.     Both  granite  and  gneiss  are  char- 
acterized by  low  toughness  and  high  hardness  with  resist- 
ance to  abrasion  somewhat  lower  than  for  trap  rock.    Their 


Physical  Properties  19 

specific  gravity  averages  close  to  2.7  and  is  seldom  less  than 
2.6  nor  more  than  2.8. 

22.  Limestone.    Limestone,  including  dolomite  and  mar- 
ble, is  usually  a  crystalline  rock  varying  in  color  from  almost 
pure  white  to  dark  grayish  black.     The  very  soft  varieties 
are,  however,  of  a  chalky  nature.    It  consists  essentially  of 
calcite,  dolomite,  or  both,  with  usually  a  small  amount  of 
quartz.     Its  free  effervescence  when  treated  with  strong 
hydrochloric  acid  and  the  fact  that  it  can  be  scratched  with 
a  knife  serve  to  identify  it.    Limestone  runs  usually  much 
lower  in  hardness,  toughness,  and  resistance  to  wear  than  do 
the  traps,  and  granites,  and  is  about  the  same  as  gneisses. 
Its  cementing  value  is,  however,  good.      The  specific  grav- 
ity of  limestone  averages  about  2.7  and  is  seldom  less  than 
2.6  or  higher  than  2.9.     Marble  averages  somewhat  higher 
than  2.7  specific  gravity. 

23.  Sandstone  and  Quartzite.     Sandstone  and  its  meta- 
morphosed equivalent,  quartzite,  are  composed  of  gains  of 
sand    bound    together    by    a    cementing   material.      They, 
therefore,  consist  chiefly  of  quartz,  although  other  minerals 
such  as  feldspar  and  mica  are  usually  present  in  appreciable 
quantity.     They  vary  from  fine  to  coarse  grain  and  exhibit 
a  number  of  colors,  the  most  common  shades  being  gray, 
white  to  buff,  brown,  and  red.     The  grains  of  sandstones 
may  be  loosely  bound  or  strongly  bound  together  and  their 
physical    properties,    therefore,    vary    widely.      Quartzite 
differs  from  sandstone  mainly  in  its  greater  hardness  and 
toughness,  density  and  crystalline  character.     Its  fracture 
shows  a  more  vitreous  luster  and  Uuually  passes  through 
the  individual  sand  grains  instead  of  between  them,  as  in 
the  case  of  sandstone.     The  specific  gravity  of  sandstone 
varies  between  wide  limits,  but  usually  lies  between  2.4  and 
2.8  with  an  average  of  a  little  more  than  2.6.    The  specific 
gravity  of  quartzite  usually  lies  between  2.6  and  2.8. 

24.  Chert.     Chert,  also  known  as  flint,  and,  in  the  form 
of  tailings  from  zinc  and  other  ores,  as  chats,  is  a  hard  non- 


20  Broken  Stone 

crystalline  or  amorphous  rock  which  breaks  with  a  con- 
choidal  fracture.  It  varies  in  color  from  light  gray  to  black. 
Owing  to  its  tendency  to  fracture  along  lines  which  have 
developed  as  shrinkage  cracks  in  the  rock  structure,  it 
frequently  shows  a  low  resistance  to  abrasion  and  is  ex- 
tremely difficult  to  test  for  toughness.  The  cementing 
value  of  fine  chert  is  usually  low,  but  some  highly  weathered 
deposits  develop  good  cementing  value,  especially  if  a  high 
binding  clay  is  associated  with  it.  Its  specific  gravity  ordi- 
narily lies  between  2.4  and  2.65. 

25.  Fieldstone  and  Congtomerates.     Field  stones  are  apt 
to  possess  extremely  variable  physical  properties  as  they 
are  composed  of  various  types  of  rock  which  have  been 
deposited    by    glacial,  action    or    by   surface    weathering. 
Conglomerates   and   breccias  are  likely  to  show  a  similar 
variation    in    properties.     The    former    are    rounded  frag- 
ments of  rock  cemented  together   in   the  rock  mass  and 
the*  latter  are  angular  fragments  similarly  held  together. 
Pudding  stone  is  a  name  given  to  certain  conglomerates. 

26.  Schist,  Shale  and  Slate.     Schists,  shales  and  slates 
possess  a  highly  laminated  or  stratified  structure  and  tend 
to  break  into  flat  plates.     They  are  seldom  suitable  for 
road-building  purposes  except  perhaps  as  a  filling  for  sub- 
foundations.      They   vary   greatly   in   nearly   all    of   their 
physical   properties. 

27.  Relative   Properties   of   Important   Rocks,     (a)  The 
relative   physical   properties   of  the  most  important  road- 
building  rock  are  diagrammatically  shown  in  Figs.  1   to  3. 
These  diagrams  represent  the  results  of  a  large  number  of 
tests  made  in  the  laboratories  of  the  U.  S.  Bureau  of  Public 
Roads. 

(b)  In  Fig.  1  is  shown  the  percentage  of  total  samples 
tested,  giving,  results  at  or  above  various  values  for  the 
French  coefficient  of  wear,  for  the  four  principal  groups 
of  road-building  rock.  It  will  be  noted  that  75  per 
cent  of  all  samples  give  a  French  coefficient  of  wear 


Physical  Properties 


21 


above  7  and  that  50  per  cent  give  a  coefficient  above  9. 
The  curve  for  trap  shows  the  highest  values,  and  it  is 
evident  that  in  a  trap  reck  country  specification  require- 
ments may  consistently  be  made  more  rigid  than  where 
other  types  predominate. 


100  75  50  25 

PER  CENT  SAMPLES  AT  OR  ABOVE 
FRENCH    COEFFICIENT 

Fig.  1     Resistance  of  Rock  to  Abrasion  or  Wear 


(c)  Fig.  2  shows  toughness  values  for  the  four  rock 
groups  in  the  same  manner  as  the  French  coefficient  of 
wear  is  shown  in  Fig.  1.  In  general  it  will  be  noted  that 
the  relative  positions  of  the  curves  in  both  figures  are 
similar,  although  the  limestones  and  granites  and  gneisses 
run  closer  together.  Over  fifty  per  cent  of  all  samples 
show  a  toughness  of  8  or  more. 


22 


Broken  Stone 


(d)  A  fairly  well-defined  relation  between  the  properties 
of  hardness  and  toughness  has  been  established  which  is 
shown  by  Fig.  3  in  which  coefficients  for  hardness  for  all 
types  of  rock  are  plotted  against  their  respective  toughness. 


60 


100  75  60  25  0 

PER  CENT  SAMPLES  AT  OR  ABOVE 

TOUGHNESS 
Fig.  2     Toughness  of  Rock 


15  10  0 

HARDNESS 

Fig.  3     Relation  of  Hardness  to 
Toughness 


Thus  it  is  seen  that  a  rock  having  a  toughness  of  8  will 
usually  show  a  coefficient  of  hardness  of  about  15.5.  Be- 
cause of  this  general  relation,  it  is  frequently  unnecessary 
to  specify  both  toughness  and  hardness  limits  for  road- 
building  rock. 

ROCK  TESTS 

28.  Resistance  to  Abrasion  or  Wear.    This  test,  some- 
times termed  the  Deval  Abrasion  Test,  has  been  adopted 


Rock  Tests  23 

by  the  American  Society  for  Testing  Materials  as  Stand- 
ard D  2-08:  Five  kilograms  (11  pounds)  of  freshly  broken 
rock  between  2  and  2J  inches  in  size  is  tested  in  a  special 
form  of  cylinder  so  mounted  on  a  frame  that  the  axis  of 
rotation  of  the  cylinder  is  inclined  at  an  angle  of  30°  with 
the  axis  of  the  cylinder  itself.  The  fragments  of  rock  form- 
ing the  charge  are  thus  thrown  from  end  to  end  twice  dur- 
ing each  revolution,  causing  them  to  strike  and  rub  against 
esrch  other  and  the  sides  of  the  cylinder.  After  10,000 
revolutions  the  resulting  material  is  screened  through  a 
iVinch  sieve  and  the  weight  of  the  material  passing  is  used 
to  calculate  the  per  cent  of  wear.  The  French  coefficient 
of  wear  is  calculated  from  the  per  cent  of  wear  as  folllows: 

40 
French  coefficient  of  wear  =  - 

Per  cent  wear 

It  will  be  seen  that  by  this  formula  the  French  coefficient 
decreases  as  the  per  cent  of  wear  increases.  A  high  French 
coefficient,  therefore,  indicates  a  low  per  cent  of  wear. 

29.  Toughness.    The    test    for    toughness    of    rock    has 
been  adopted  by  the  American  Society  for  Testing  Materials 
as  Standard  D  3-18.    Toughness  is  determined  by  subject- 
ing a  cylindrical  test  specimen  25  by  25  millimeters  (1  by  1 
inch)  in  size  to  the  impact  produced  by  the  fall  of  a  2-kilo- 
gram (4.4  pound)  hammer  upon  a  steel  plunger  whose  lower 
end  is  spherical  and  rests  upon  the  test  piece.    The  energy 
of  the  blow  delivered  is  increased  by  increasing  the  height 
of  fall  of  the  hammer  1  centimeter  (0.39  inch)  after  each 
blow.     The  height  of  blow  in  centimeters  at  failure  of  the 
specimen  is  called  the  toughness. 

30.  Hardness.    Hardness  is  determined  by  subjecting  a 
cylindrical  rock  core  25  millimeters  (1  inch)  in  diameter, 
drilled  from  the  specimen  to  be  examined,  to  the  abrasive 
action  of  quartz  sand  fed  upon  a  revolving  steel  disk  during 
1000  revolutions.     The  end  of  the  specimen  is  worn  away 
in  inverse  ratio  to  its  hardness  and  the  amount  of  loss  is 


24  Broken  Stone 

expressed  in  the  form  of  a  coefficient  according  to  the  fol- 
lowing formula  in  which  w  is  the  loss  in  weight. 

w 
Coefficient  of  hardness  =  20  —  —  • 

o 

From  this  formula  it  is  seen  that  the  higher  the  coefficient 
the  harder  is  the  rock. 

31.  Cementing  Value.     To  determine  the  binding  power, 
or  cementing  value,  as  it  is  usually  called,  500  grams  (1.1 
pounds)  of  the  material  to  be  tested  is  crushed  to  pea  size 
and  ground  with  water  in  a  ball  mill  until  it  has  the  con- 
sistency of  a  stiff  dough.    It  is  then  moulded  into  cylindrical 
briquettes  25  by  25  millimeters  (1  by  1  inch)  in  size,  which, 
after  thorough  drying,  are  tested  to  destruction  in  a  special 
form  of  impact  machine.    A  1-kilogram  (2.2-pound)  hammer 
falls  through  a  constant  height  of  1  centimeter  (0.39  inch) 
upon  an  intervening  plunger,  which  in  turn  rests  upon  the 
test  piece.    By  means  of  a  suitable  arrangement  a  graphic 
record  of  the  number  of  blows  required  to  destroy  the  speci- 
men is  obtained.     The  number  of  blows  producing  failure 
is  called  the  cementing  value  of  the  material. 

32.  Size  or  Grading.     The  size  or  grading  of  broken  stone 
products   is   ascertained   by   making   a   mechanical   screen 
analysis.     This  may  be  done  by  the  Inspector  (§371),  the 
Laboratory,  or  both.    A  dry  sample  of  the  product  weigh- 
ing not  less  than  fifty  times  the  weight  of  the  largest  stone 
present  is  passed  through  screens  having  circular  openings, 
as  are  required  or  called  for  by  the  specifications.    Starting 
with  the  screen  with  largest  openings,  the  percentage  by 
weight  retained  on  each  screen  and  the  percentage  passing 
the  screen  with  smallest  openings  is  recorded. 

33.  Specific  Gravity,  Weight  per  Cubic  Foot,  Absorption. 
(a)  There  are  a  number  of  methods  for  making  this  determi- 
nation.    The  American  Society  for  Testing  Materials  has 
adopted  standard  test  D  30-18  for  determination  of  apparent 
specific  gravity  of  coarse  aggregates,  which  may  be  briefly 


Rock  Tests  25 

described  as  follows:  A  1000-gram  sample  composed  of 
suitably  sized  fragments  is  dried  and  weighed.  It  is  then 
immersed  in  water  for  24  hours  and  again  weighed.  Its 
weight  under  water  suspended  in  a  wire  basket  is  next  ascer- 
tained. The  specific  gravity  of  the  sample  is  then  calcu- 
lated by  means  of  the  following  formula  in  which  A  is  the 
weight  of  the  dry  sample,  B  the  weight  of  the  saturated 
sample  in  air,  and  C  its  weight  in  water, 

Sp.  Gr. 


B  -C 

A  similar  method  may  be  used  by  the  Inspector  (§  376)  in 
the  field  for  obtaining  a  rough  determination. 

(6)  The  absorption  of  the  rock  is  obtained  on  a  percentage 
basis  as  follows: 

100(B  -  A) 

Per  cent  absorption  =  -  —  • 

A 

(c)  Sometimes  the  results  of  the  specific  gravity  and 
absorption  tests  are  reported  upon  the  basis  of  pounds  per 
cubic  foot  of  solid  rock.  In  this  case  the  weight  per 
cubic  foot  equals  the  specific  gravity  multiplied  by 
62.4.  The  absorption  in  pounds  per  cubic  foot  equals  the 
per  cent  of  absorption  multiplied  by  the  weight  per  cubic 
foot. 

34.  Determination  of  Voids.  Voids  in  a  broken  stone 
aggregate  after  compaction  by  settlement  may  be  ascer- 
tained by  measuring  the  volume  of  water  required  to  fill 
the  interstices  of  a  known  volume  01  compacted  aggregate. 
The  per  cent  of  voids  is  calculated  by  dividing  this  volume 
of  water  by  the  apparent  volume  of  the  aggregate.  If  the 
specific  gravity  of  the  aggregate  is  known,  the  per  cent  of 
voids  may  also  be  determined  by  dividing  the  weight  of  a 
given  volume  of  the  aggregate  by  the  calculated  weight  of 
the  same  volume  of  the  solid  rock  and  subtracting  this 
result  from  1.00  (§377). 


26  Broken  Stone 

MEASUREMENT 

35.  Weight  Basis.    Broken  stone  is  most  frequently  pur- 
chased and,  therefore,  measured  by  weight.     While  this  is 
usually  a  satisfactory  basis  there  are  two  factors  which  the 
Inspector  should  bear  in  mind.     One  is  that  the  weight  of 
broken  stone  is  not  necessarily  a  constant,  and  the  other 
that  considerable  difference  in  volume  may  be  represented 
by  the  same  weight.     In  connection  with  the  former,  the 
weight  of  perfectly  dry  rock  may  be  increased  by  absorp- 
tion of  water  amounting  in  some  limestones  to  as  high  as 
13  per  cent.    To  this  may  be  added  water  which  is  mechani- 
cally held  on  the  surface  of  the  individual  fragments  of  the 
aggregate   which,   as   determined  -in   the   laboratory,   may 
amount  to   over   1   per   cent  for  very  wet  rock.     Freight 
weights  are  usually  accepted  as  a  basis    for  payment   if 
shipment  is  made  by  rail,  but  in  all  cases  it  should  be  under- 
stood that  original  weights  are  to  be  on  the  basis  of  air-dry 
products.     The  relation  of  volume  to  weight  is  considered 
in  paragraphs  36  -and  37. 

36.  Volume  Basis.    While  the  volume  of  broken  stone 
is  perhaps  the  most  satisfactory  basis  for  estimating  the 
amount  of  road  or  pavement  to  be  or  which  has  been  con- 
structed, the  fact  that  the  volume  of  an  aggregate  is  not  a 
constant   makes   it   an   unsatisfactory   basis   for   purchase. 
Thus  a  given  weight  of  rock  when  first  loaded  upon  a  freight 
car  will  occupy  considerably  more  space  than  when  received 
at  its  destination,  due  to  settlement  or  reduction  in  voids 
in  transit.    If  purchased  upon  a  volume  basis  the  place  and 
the  conditions  under  which  measurement  is  made  should 
be  clearly  understood  in  advance.     Under  the  same  condi- 
tions the  relation  of  weight  to  volume  of  a  given  broken- 
stone  product  is  a  constant,  so  that  a  cubic  yard  may  be 
assigned  a  definite  weight.     When,  however,  a  variety  of 
rocks  is  considered,  it  is  evident  that  the  specific  gravity  of 
the  rock  will  considerably  affect  its  weight  per  cubic  yard. 


Measurement  27 

Thus,  if  a  cubic  yard  of  broken  stone  with  a  specific  gravity 
of  2.6  weighs  2600  pounds,  a  cubic  yard  of  the  same  grade 
of  product  in  the  same  state  of  compaction  for  a  rock  of 
3.0  specific  gravity  would  be  3000  pounds  per  cubic  yard, 
thus  making  a  difference  of  400  pounds  per  cubic  yard. 
Where  rocks  of  such  a  range  of  specific  gravity  are  allowed 
to  be  used  in  a  given  contract  it  is  evident  that  the  weight 
of  rock  required  may  vary  appreciably  and  that  the  actual 
weight  used  is  no  true  measure  of  work  done  unless  the 
specific  gravity  of  the  product  is  known.  To  illustrate: 
if  a  given  weight  of  broken  stone  of  3.0  specific  gravity  will 
build  13  miles  of  road,  the  same  weight  of  broken  stone  of 
2.6  specific  gravity  will  build  15  miles  of  road.  Such  a 
difference  is  worth  some  consideration  if  the  stone  is  pur- 
chased upon  a  weight  basis. 

37.  Voids,  (a)  It  has  been  stated  that  the  volume  of 
broken  stone  is  not  a  constant  because  of  settlement  or 
reduction  in  voids.  In  any  broken-stone  product  the  per 
cent  of  voids  will  depend  principally  upon  two  factors:  the 
grading  of  the  aggregate  and  its  degree  of  compaction.  In 
general,  the  percentage  of  voids  is  greatest  when  the  frag- 
ments are  of  uniform  size  and  have  not  been  closely  packed 
by  settlement  or  pressure.  They  are  least  when  the  frag- 
ments are  so  graded  that  for  a  given  volume  of  the  larger 
sized  fragments  there  are  just  sufficient  smaller  particles 
to  fill  the  interstices,  and  when  all  of  the  particles  are  brought 
into  the  most  intimate  contact  possible  through  compaction. 
For  the  average  commercial  broken-stone  product  of  fairly 
uniform  size  numerous  tests  have  shown  that  when  loose 
and  uncompacted  by  travel,  also  in  thin  layers,  the  voids 
are  approximately  50  per  cent;  under  light  compaction  or 
travel  and  in  thick  masses,  they  are  about  45  per  cent;  and 
when  compacted  by  heavy  travel,  shaking  or  high  drop  they 
are  40  per  cent.  Forty  per  cent  voids  represent  about  the 
maximum  compaction  without  rolling.  This  makes  a  con- 
venient basis  for  figuring  pounds  per  cubic  yard  which  is 


28 


Broken  Stone 


then  for  all  practical  purposes  2000  times  the  specific 
gravity  of  the  rock.  Thus  a  rock  of  2.7  specific  gravity 
with  40.5  per  cent  voids  will  weigh  2700  pounds  per  cubic 
yard. 

(6)  For  the  purpose  of  estimating  quantities  needed  or 
amount  used  of  a  given  commercial  size,  the  following  per- 
centage of  voids  may  be  assumed: 


4500 

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2500 

*^*^ 

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^^^^\ 

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7^\ 

O^*** 

^-  — 

+^*^~ 

——^ 

^^_ 

20002 

A 

2 

6 

2. 

8 

3 

.0 

3.2 

SPECIFIC  GRAVITY 
Fig.  4     Weight  of  Broken  Stone 


Loose  piles  or  very  thin  layersl  ji;h>T-vuctia'X  .o^i 
Loose  spread  water  bound  macadam  ......... 

Coarse  aggregate  for  Portland  Cement  Concrete 

Coarse  aggregate  for  Graded  Bituminous  Con- 

crete compacted  ............  ............. 

Crusher  run,  loose,  without  segregation  ....... 

Rolled  broken  stone  ....................... 

Crusher  run,  compacted  .................... 


50  per  cent 
45    "      " 

40  "  " 

35  "  " 

30  "  " 

20  H  " 


Sampling  29 

The  approximate  weight  per  cubic  yard  and  number  of 
cubic  yards   per   100   tons   for   broken   stone   of   different 


100 
90 

UJ 

^~  

R  100  TONS 

§ 

—  ^S; 

^=j 

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2 

4 

2. 

6 

2. 

8 

3 

0 

3.2 

SPECIFIC  GRAVITY 
Fig.  5     Volume  of  Broken  Stone 

specific  gravities  and  the  various  percentages  of  voids  above 
mentioned  are  shown  in  Figures  4  and  5. 

SAMPLING 

38.  Time  and  Place  of  Sampling.  Samples  of  rock  or 
broken  stone  may  be  taken  at  any  time  before  or  during  its 
use.  When  the  specifications  require  physical  properties 
which  must  be  determined  by  laboratory  test,  a  preliminary 
sample  should  be  taken  from  each  proposed  source  of  supply 
at  least  two  weeks  before  final  acceptance.  However,  in 


30  Broken  Stone 

the  case  of  well-known  sources  of  supply,  from  which  the 
material  has  been  tested  and  approved  within  one  year, 
the  preliminary  sample  may  be  omitted  at  the  discretion  of 
the  Engineer.  When  stone  from  an  approved  source  of 
supply  is  being  used  and  does  not  appear  equal  in  quality  to 
the  original  sample  or  to  that  previously  furnished,  it  should 
be  resampled  immediately.  Broken  stone  may  be  sampled 
for  size  or  grading  at  the  crusher,  from  bins,  cars,  or  from 
storage  piles  on  the  job.  Frequent  samples  should  be  taken 
on  the  job  and  tested  by  the  inspector  (§371)  when  the 
grading  is  an  important  factor. 

39.  Sampling  for  Quality,  (a)  When  sampling  from 
quarry  or  ledge  care  must  be  taken  that  the  sample  repre- 
sents sound,  fresh,  interior  stone.  Such  material  may  be 
secured  either  by  blasting  or  breaking  up  with  a  sledge. 
Rotten,  partially  disintegrated  or  weathered  specimens 
should  not  be  taken.  If  all  material  in  the  deposit  is  essen- 
tially of  the  same  variety  and  texture,  a  single  sample  will 
be  sufficient.  If,  however,  the  material  occurs  in  layers  or 
differs  in  variety  or  texture  at  different  points  in  the  deposit, 
separate  samples  should  be  taken  of  each  apparent  variety. 
In  the  latter  case  the  relative  proportion  of  each  variety  in 
the  deposit  should  be  reported.  Mixed  samples  or  samples 
representing  two  or  more  varieties  should  be  taken  only 
when  especially  directed,  in  which  case  the  relative  propor- 
tion of  the  different  varieties  in  the  sample  should  be  made 
as  nearly  as  possible  the  same  as  the  proportions  in  which 
they  occur  in  the  deposit.  It  is  advisable  for  the  Inspector 
to  retain  a  small  specimen  representative  of  the  rock  sampled 
to  be  used  as  a  guide  in  inspecting  shipments  of  the  material 
if  approved.  In  the  case  of  field  stone,  when  two  or  more 
varieties  of  great  difference  in  quality  or  texture  are  ob- 
served, separate  samples  should  be  taken  of  each  and  the 
percentage  of  each  kind,  together  with  the  relative  amount 
of  disintegrated  or  badly  weathered  rock  present,  should  be 
reported.  It  is  also  advisable  to  report  the  relative  amount 


Sampling  31 

of  small  stone  which  might  be  expected  to  pass  through  the 
crusher  without  breaking. 

(b)  Each  sample  for  the  abrasion  test  should  weigh  be- 
tween 25  and  35  pounds,  the  fragments  being  two  inches 
or  more  in  diameter,  unless  the  sample  is  taken  from  the 
crusher  output,  in  which  case  15  pounds  of  fragments  averag- 
ing 2  to  2J  inches  in  diameter  will  be  sufficient.  If  a  tough- 
ness or  hardness  test  is  necessary  one  fragment  measuring 
at  least  3  by  4  by  6  inches  will  be  required.  This  piece 
should  be  free  from  seams  and  cracks. 

40.  Sampling  for  Size  or  Grading.  When  sampling  for 
size  or  grading  a  composite  sample  of  each  product,  com- 
posed of  samples  taken  from  different  parts  of  the  supply, 
should  be  taken.  This  precaution  is  necessary  because 
of  the  general  tendency  of  fragments  of  the  same  size  to 
segregate.  When  they  are  to  be  shipped  to  the  laboratory 
composite  samples  should  weigh  about  ten  pounds  for 
aggregates  containing  fragments  f  inch  in  diameter  or  less 
and  samples  of  larger  aggregates  should  increase  in  size  up 
to  60  or  75  pounds  (§  153).  In  general  a  sample  should 
weigh  not  less  than  fifty  times  the  weight  of  the  largest 
fragment  present.  When  sampling  a  number  of  cars  or 
piles  of  supposedly  the  same  product,  an  individual  com- 
posite sample  should  be  taken  from  each  car  or  pile  the  size 
or  grading  of  which  is  apparently  different  from  the  others. 


CHAPTER  III 
GRAVEL,  SAND  AND  CLAY 

JJ£jnjj>.jVi:  7  fiVyrj 

NATURAL  ROCK  PRODUCTS 

-,    •>:T-    iii!i:   >.IHJ;'>X    [|ft?-!';    •»'/]''    •  ,<  {    |)|j-, 

41.  Occurrence.    Under    prolonged    action    of    the    ele- 
ments  massive   rock   disintegrates    and    frequently   suffers 
decomposition  and  so  produces  soils.     Thus,  frost  action 
may  result  in  the  splitting  or  breaking  up  of  rock  masses 
while  the  action  of  ground  waters  may  produce  chemical 
changes  in  the  constituent  minerals,  resulting  in  alteration 
of  the  rock  structure.     Fragments  of  rock  and  decompo- 
sition products  have  in  certain  cases  remained  at  or  near 
their  place  of  formation  and,  in  other  .  cases,   have  been 
transported  for   long  distances   by  water,  wind   or  glacial 
action.    When  rock  fragments  remain  at  or  near  their  place 
of  formation  they  become  weathered   or  rotten   under  at- 
mospheric influences  and  are  usually  unsuitable  for  highway 
construction.     If  transported  the  surface  of  individual  frag- 
ments usually  becomes  polished  by  abrasive  action  and  often 
rounded,  while  soft   decomposition   products   are   removed. 
As  they  are  eventually  deposited  by  the  force  of  gravity, 
fragments  of  approximately  the  same  size  and  weight  tend 
to  separate  or  segregate  from  fragments  of  different  size  or 
weight.    While  such  segregation  is  seldom  complete,  deposits 
frequently  show  a  preponderance  of  fragments  within  certain 
ranges  of  size  which  are  used  as  a  basis  for  classification. 
These  deposits  may  occur  locally  as  beds  of  lakes  or  rivers, 
or  in  banks  or  beds  forming  a  part  of  the  earth's  surface. 

42.  Classification.     The   fact   that   the    greatest   variety 
of  different  size  fragments  in  all  combinations  of  relative 

32 


Gravel  33 

proportion  occurs  in  natural  soil  deposits  makes  the  matter 
of  their  classification  extremely  difficult,  and  no  standard 
of  classification  has  been  generally  adopted  by  highway 
engineers.  Any  specification  calling  for  gravel  or  sand  in 
particular  should,  therefore,  define  the  terms  for  that  speci- 
fication. Where  specifications  are  indefinite  the  following 
class  limits  based  upon  field  or  laboratory  test  may,  how- 
ever, prove  of  service  to  the  Inspector: 

Boulders.     Fragments   with  a   maximum  diameter    of   6 

inches  or  more. 
Gravel.     All  fragments  which  will  be  retained  on  a  f-inch 

screen. 
Sand.     All  fragments  which  will  pass  a  J-inch  screen  and 

be  retained  on  a  200-mesh  sieve. 
Silt.     All  particles  which  will  pass  a  200-mesh  sieve  and 

will  not  be  removed  by  elutriation. 
Clay.     All  inorganic  matter  which  will  be  removed  by 

elutriation. 

While  the  above  limits  will  serve  to  distinguish  between 
the  constituents  of  a  natural  deposit,  they  do  not  classify 
the  combinations  commonly  found.  Such  classification  is 
taken  up  under  separate  headings  for  gravel,  sand,  and  clay. 

GRAVEL 

43.  Types  of  Gravel,  (a)  Pebbles  of  gravel  in  a  given 
deposit  may  be  and  most  frequently  are  composed  of  a 
variety  of  rocks,  although  a  given  rock  family  or  group 
usually  predominates.  The  name  cf  the  predominating 
rock,  if  there  be  one,  is  commonly  assigned  to  the  product, 
so  that  the  terms  trap  gravel,  granite  gravel,  limestone 
gravel,  quartzite  or  quartz  gravel,  and  sandstone  gravel  are 
not  infrequently  used.  The  general  nature  of  the  deposit 
is  also  used  to  designate  gravel,  the  most  common  terms 
being  glacial  gravel,  bank  or  pit  gravel,  river  gravel,  and 
lake  gravel. 


34  Gravel,  Sand  and  Clay 

(6)  In  addition,  gravels  or  gravel  deposits  are  roughly 
classified  by  the  proportion  and  nature  of  other  constitu- 
ents which  may  be  present.  The  most  important  types 
from  this  standpoint  are  the  sand  or  sandy  gravel,  the 
sand-clay  gravel,  and  the  clay  gravel.  In  general  gravel 
deposits  may  be  considered  as  deposits  containing  less 
than  fifty  per  cent  of  boulders  or  cobbles  and  a  percentage 
of  gravel  greater  than  the  per  cent  of  all  other  constituents 
combined.  Sandy  gravel  is  gravel  in  which  the  proportion 
of  combined  sand  and  silt  to  clay  is  greater  than  10:  1. 
Clay  gravel  is  that  in  which  the  proportion  of  combined 
sand  and  silt  to  clay  is  less  than  3 :  2.  And  sand-clay  gravel 
lies  between  the  two  last  named  varieties.  Gravel  in  which 
the  pebbles  mainly  range  from  |  to  J  inch  in  diameter  is 
sometimes  known  as  pea  gravel.  Large  gravel  pebbles  and 
small  rounded  boulders  are  sometimes  called  cobbles. 

44.  Production.     As  dug  from  a  bank  or  pit,  or  dredged 
from  the  bed  of  a  river  or  lake,  gravel  is  frequently  unsuited 
for  direct  use.    To  meet  the  requirements  of  a  given  speci- 
fication it  may  have  to  be  screened  to  remove  undesirably 
large  fragments  and  perhaps  sand  and  other  fine  material. 
It  is  sometimes  washed  for  the  latter  purpose.    It  may  also 
be  necessary  to  separate  it  into  certain  ranges  of  size  or 
grading.     When  this  is  the  case  and  the  deposit  contains 
an  appreciable  proportion  of  pebbles  larger  than  the  maxi- 
mum required  size,  a  complete  crushing  and  screening  plant 
may  be  employed  similar  to  that  used  in  the  manufacture 
of  broken  stone  (§  17).  .   , 

45.  Physical    Properties,     (a)  Specifications    for    gravel 
sometimes  specify  the  type  of  deposit  from  which  it  is  to 
be  obtained,  the  soundness  of  its  particles,   and  freedom 
from  clay,  loam,  dirt  and  coatings.     The  maximum  size  of 
individual   pebbles  is   almost   invariably   specified   and   in 
many  cases  size  or  grading  of  each  gravel  product  to  be  used 
is  covered.     Less  frequently  its  resistance  to  abrasion  arid  its 
cementing  value  or  that  of  its  finer  constituents  are  specified. 


Gravel  35 

(6)  From  the  nature  of  their  origin,  the  physical  proper- 
ties of  gravels  vary  widely.  In  general  the  toughness  and 
hardness  of  gravel  will  approximate  that  of  its  predominat- 
ing rock,  but  it  is  impracticable  to  use  the  tests  for  these 
properties  as  applied  to  rock.  Durability  under  traffic 
conditions  is  the  important  thing  to  consider  and,  in  general^ 
trap,  quartz  and  chert  gravels  are  the  most  durable.  If 
cementing  value  is  required,  a  certain  amount  of  clay  binder 
is  desirable  except  in  the  case  of  a  limestone  gravel  or  one 
containing  an  appreciable  amount  of  limestone.  Sand- 
stone gravels  because  of  their  smooth  or  polished  surfaces 
may  appear  to  be  perfectly  sound  and  highly  resistant 
to  abrasion.  Frequently,  however,  if  the  surface  is  broken, 
inferior  quality  or  unsound  rock  will  be  exposed.  Such 
gravels  rapidly  break  down  into  sand  under  traffic,  owing  to 
their  lack  of  toughness. 

(c)  The  size  of  grading  of  gravel  may  be  specified  as  in 
the  case  of  broken  stone  (§  18c).  The  most  satisfactory 
method  is  that  based  upon  screen,  or  screen  and  sieve  tests, 
which  in  many  cases  may  be  made  by  the  Inspector  (§371). 
Owing  to  the  rounded  nature  of  most  gravel  particles,  no 
interlocking  occurs  in  a  compacted  mass  as  in  the  case  of 
broken  stone.  Glacial  gravels  differ  from  others  in  the  fact 
that  the  individual  pebbles  are  more  or  less  angular.  Crushed 
gravel  resembles  broken  stone  in  its  ability  to  interlock  in 
proportion  to  the  relative  amount  of  crusher-broken  frag- 
ments which  it  contains.  When  gravel  is  composed  largely 
of  rounded  particles  mechanical  stability  in  a  road  structure 
is  obtained  only  by  the  presence  or  use  of  a  fine  aggregate 
filler  and  a  cementing  medium.  The  specific  gravity  and 
voids  in  a  gravel  product  will,  of  course,  depend  upon  the 
relative  proportion  of  different  types  of  rock  present  and 
the  grading  of  the  aggregate  which  is  extremely  variable. 
The  voids  in  gravel  which  is  screened  into  commercial  sizes 
and  the  reduction  of  voids  due  to  compaction  is  approxi- 
mately the  same  as  for  broken  stone  of  the  same  size  (§  37). 


36  Gravel,  Sand  and  Clay 

SAND 

I'.ii?:    -KHiibiR,?    -;iil    IfftotW   ill 

46.  Types  of  Sand,  (a)  As  a  rule  sand  is  of  much  more 
uniform  composition  than  gravel.  It  represents  the  sur- 
vival of  the  fittest  of  all  the  common  rock  forming  minerals 
which  is  chiefly  quartz.  The  other  minerals,  which  are 
largely  silicates  and  carbonates,  are  as  a  rule  decomposed 
during  the  reduction  of  rock  to  the  size  of  sand  grains  so 
that  by  far  the  largest  proportion  of  the  final  product  con- 
sists of  quartz  fragments  which  may  be  smooth  and  round 
or  sharp  and  angular.  There  are  some  exceptions  to  this 
rule,  however,  particularly  where  the  sand  constitutes  a  por- 
tion of  a  limestone  gravel,  in  which  case  it  is  also  composed 
mainly  of  limestone  particles.  Like  gravel,  the  general  na- 
ture of  the  deposit  may  be  used  to  designate  sand,  the  most 
common  varieties  being  glacial  sand,  bank  sand,  dune  sand, 
river  sand,  lake  sand  and  beach  sand.  . 

(6)  Sands  are  further  classified  by  the  proportion  of  other 
constituents  which  are  present.  In  general,  sand  deposits 
may  be  considered  as  deposits  containing  a  greater  percen- 
tage *of  sand  than  the  combined  percentage  of  all  other 
constituents.  A  gravelly  sand  is  one  in  which  an  appre- 
ciable proportion  of  gravel  is  present.  A  sand-clay  is  a 
mixture  of  sand  and  clay  in  which  the  proportion  of  sand 
and  silt  to  clay  lies  between  10:  1  and  3:2.  A  loamy  sand 
is  one  containing  silt,  clay  and  decomposed  vegetable 
matter  or  humus.  To  this  type,  occurring  in  fields  which 
have  been  cultivated,  the  name  top  soil  has  been  given. 
Sand  which  is  composed  principally  of  particles  which  will 
be  retained  on  a  10-mesh  sieve  is  sometimes  known  as 
torpedo  sand,  or  gravel  grit  if  the  preponderating  particles 
average  about  |  inch  in  diameter.  Concrete  sands  are 
fairly  coarse  sands,  the  largest  proportion  of  particles  being 
usually  retained  on  a  50-mesh  sieve.  Sands  for  sheet  asphalt 
are  well-graded  products  which  will  pass  a  10-mesh  sieve  and 
are  practically  free  from  silt  and  clay.  Grouting  sands  are 


Sand  37 

usually  fine  products  at  least  80  per  cent  of  which  will  pass 
a  20-mesh  sieve. 

47.  Production.    As  excavated  or  dredged  from  natural 
deposits  sand  may  not  be  directly  suited  for  use  and  may 
have  to  be  screened  to  remove  gravel  or  all  particles  over  a 
given  size.     This  is  frequently  done  by  throwing  the  sand 
against  a  string  or  wire  screen,   the  inclination  of  which 
controls  to  a  considerable  extent  the  maximum  size  particle 
which   passes.      Sands   containing   undesirable   amounts   of 
silt  and  clay,  but  otherwise  suitable,  may  have  to  be  washed 
after  removal  from  the  deposit.     If  clay  or  organic  matter 
actually  coats  the  sand  grains  and  does  not  exist  mainly 
as  a  void  filler,  washing  the  sand  will  seldom  produce  a 
satisfactory  product.     If  the  grading  of  the  sand  is  not 
satisfactory  it  is  sometimes  mixed  with  another  selected 
sand  in  such  proportions  as  to  produce  the  desired  grading. 
This  operation  is  usually  conducted  at  or  near  the  place 
where  the  sand  is  to  be  used,  as  for  instance,  a  paving  plant. 
In  some  cases  it  may  be  necessary  to  mix  clay  with  the 
sand  or  to  add  a  fairly  clean  sand  to  one  containing  more 
than  the  desirable  percentage  of  clay.     Such  mixtures,  in- 
tended to  produce  a  sand-clay  suitable  for  highway  pur- 
poses, are  prepared  in  place  on  the  road,  one  constituent 
being  the  natural  soil  existing  at  such  place. 

48.  Physical  Properties,     (a)  Specifications  for  sand  fre- 
quently specify  the  soundness  and  durability  of  the  indi- 
vidual grains  as  well  as  their  freedom  from  coatings  of  clay 
or  loam.     The  general  type  of  grains,  whether  round  or 
sharp,  is  sometimes  stipulated,  together  with  the  absence 
of  dirt  and  other  foreign  matter.    The  grading  of  the  sand 
is  usually  covered  in  some  manner,  often  in  considerable 
detail,  and  for  some  types  of  work  the  allowable  or  neces- 
sary percentages  of  gravel,  silt  or  clay  are  included.    The 
cementing  value  of  the  product  may  also  be  specified  and 
in  rare  instances  its  resistance  to  abrasion.     The  tensile 
strength  imparted  to  Portland  cement  mortar  in  which  it 


38  Gravel,  Sand  and  Clay 

is  used  is  quite  often  included  in  specifications  for  sand  to 
be  used  in  concrete  construction. 

(6)  Because  of  its  method  of  formation  and  usual  com- 
position, the  durability  of  sand  or  its  resistance  to  abrasion 
is  high.  In  exceptional  cases  such  as  limestone  sands,  resist- 
ance to  abrasion  is  a  variable  quantity  which  may  be  de- 
termined by  test  (§  51).  When  sand  is  associated  with 
clay  or  organic  matter,  such  material  may  exist  merely  as 
a  void-filling  medium  for  the  clean  sand  grains  or  a  portion 
may  become  firmly  attached  as  a  coating.  This  may  be 
ascertained  by  means  of  a  magnifying  glass  or  microscope. 
Coated  sands  are  unsuitable  for  use  when  they  are  to  be 
mixed  with  hydraulic  or  bituminous  cements,  as  the  coating 
interferes  with  the  bond  which  it  is  desired  to  secure  in 
such  mixtures.  The  presence  of  an  appreciable  amount  of 
organic  matter  existing  either  as  a  coating  or  void  filler  is 
considered  injurious  if  the  sand  is  to  be  used  with  hydraulic 
cement.  An  appreciable  amount  of  mica  is  also  considered 
undesirable,  particularly  if  a  dense  product  is  required,  as  the 
fiat  plates  of  this  mineral  tend  to  prevent  the  sand  grains 
from  packing  together  as  closely  as  they  otherwise  would. 
The  cementing  value  of  a  sand  will  depend  almost  entirely 
upon  the  quantity  and  character  of  clay  which  may  be 
present.  Pure  quartz  sand  shows  practically  no  cementing 
value  by  test.  Limestone  or  carbonate  sands  are,  however, 
an  exception  and  may  develop  good  cementing  value  even 
if  clay  is  absent. 

(c)  The  size  or  grading  of  sand  is  usually  specified  upon 
the  basis  of  laboratory  screens  and  sieves,  and  is  frequently 
a  most  important  consideration  in  highway  construction 
with  relation  to  density,  stability  and  workability.  No 
matter  what  its  grading  or  state  of  compaction,  clean  dry 
sand  is  unstable  or  readily  subject  to  displacement.  Com- 
pacted wet  or  saturated  sand  may,  however,  possess  con- 
siderable stability,  depending  upon  its  size  and  grading.  If 
all  of  its  particles  are  approximately  of  the  same  size,  as  in 


Sand 


39 


the  case  of  quicksands,  it  is  unstable  in  either  the  wet  or 
dry  state.  The  percentage  of  voids,  and,  therefore,  the 
weight  per  unit  volume  of  sand,  is  largely  governed  by  its 
grading  and  moisture  content,  as  well  as  its  degree  of  com- 
paction. The  presence  of  moisture  in  particular  interferes 
with  compaction  to  a  very  material  extent  and  within  cer- 
tain limits  its  addition  to  sand  will  cause  swelling  or  increase 


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PER  CENT  VOIDS 
Fig,  6     Weight  and  Volume  Relations  for  Dry  Quartz  Sand 

in  volume.  This  is  due  to  the  fact  that  in  moist  sand  a  film 
of  water  coats  each  particle  and  by  surface  tension  sepa- 
rates it  from  the  surrounding  particles.  This  effect  is  so 
pronounced  that  with  the  added  weight  of  water  present, 
moist  sand  will  weigh  materially  less  per  cubic  yard  than 
the  same  sand  dry.  It  is  most  important  that  the  Inspector 
bear  this  fact  in  mind  in  the  measurement  of  quantities  and 


40  Gravel,  Sand  and  Clay 

proportions.  The  effect  of  moisture  is  a  variable  depending 
upon  the  composition  and  grading  of  the  sand.  Between 
3  and  10  per  cent  of  moisture  will  usually  produce  the 
maximum  difference  which  experiments  have  demonstrated 
may  be  as  high  as  12  per  cent  voids  or  over  500  pounds  per 
cubic  yard.  After  the  maximum  effect  of  moisture  is  pro- 
duced the  further  presence  of  water,  owing  to  its  lubricating 
properties,  begins  to  decrease  the  percentage  of  voids,  until 
finally  very  wet  sand  will  occupy  less  space  than  the  dry 
sand  under  similar  methods  of  compaction.  Hot,  dry  sand 
will  weigh  less  per  unit  volume  than  will  unheated  dry 
sand.  Thus  a  sheet  asphalt  sand  which  may  weigh  111 
pounds  per  cubic  foot  cold  may  when  hot  weigh  as  low  as 
95  pounds  per  cubic  foot.  This  is  due  to  separation  of  the 
fine  particles  by  films  of  expanded  hot  air.  Like  gravel, 
sand  is  usually  measured  and  purchased  upon  a  volume 
basis.  The  specific  gravity  of  quartz  sand  is  about  2.65 
or  approximately  the  same  -as  pure  quartz.  Its  percentage 
of  voids  will  usually  lie  between  25  and  50  per  cent.  Upon 
this  basis  Fig.  6  shows  the  weight  and  volume  relations  of 
dry  quartz  sand. 

CLAY 

.  ^J 


49.  Types  of  Clay.  Clay  is  composed  of  decomposition 
products  of  rock-forming  minerals,  and  may  be  either  re- 
sidual or  transported.  It  commonly  occurs  in  banks  or  beds 
above  or  below  water.  For  highway  purposes  it  may  be 
classified  by  the  proportion  of  other  constituents  which-  are 
present  and,  in  a  general  way,  by  its  variations  in  the 
properties  of  plasticity  and  slaking.  In  general  clay  de- 
posits may  be  considered  as  deposits  containing  a  greater 
percentage  of  clay  than  the  combined  percentage  of  all  other 
constituents.  .  A  sandy  clay  is  one  in  which  an  appreciable 
proportion  of  sand  or  sand  and  silt  is  present.  Calcareous 
clay  contains  an  appreciable  percentage  of  calcium  car- 
bonate, and  if  the  percentage  of  this  constituent  is  relatively 


Tests  41 

high,  the  product  becomes  marl.  Gumbo  is  a  type  of  clay 
containing  a  high  percentage  of  decayed  vegetable  or 
organic  matter  and  very  little  sand  or  silt,  while  loam  is 
composed  of  clay  and  sand  mixed  with  considerable  vege- 
table matter  or  humus.  A  lean  clay  is  a  non-plastic,  rapid 
slaking  clay  containing,  as  a  rule,  considerable  silt,  and  a 
fat  clay  is  highly  plastic,  slow  slaking,  and  contains  rela- 
tively little  silt. 

50.  Properties.     The  physical  properties  of  clay,  as  such, 
are  seldom  included  in  highway  specifications,  but  the  per- 
centage of  clay  in  other  products  is  frequently  covered  and 
the  minimum  cementing  value  of  the  whole  or  a  certain  por- 
tion of  such  products,   depending  upon  the  amount   and 
character  of  clay  present,  is  also  occasionally  specified.    The 
specific  gravity  of  pure  dry  clay  varies  with  its  composition. 
The  weight  per  cubic  yard  for  clay  is  frequently  assumed 
as  2700  pounds,  but  as  most  clays  are  highly  retentive  of 
water  and,  as  ordinarily  used,  vary  greatly  in  their  water 
content,    their   weight   will   also   vary   within   wide   limits. 
When  in  a  very  finely  divided  and  perfectly  dry  state,  clays 
fluff  up  and  may  weigh  as  low  as  75  pounds  per  cubic  foot 
or  2025  pounds  per  cubic  yard.     Clays  vary  greatly  in  the 
property  of  plasticity  or  their  ability  to  form  pasty  masses 
when  wet.     As  a  rule,  except  with  carbonate  clays,  high 
plasticity  accompanies  high  cementing  value  and  vice  versa. 
Chemical  composition,  color,  fusibility  and  shrinkage  from 
plastic  to  dry  condition  are  important  considerations  from 
the    standpoint    of    paving    brick    manufacture,   but    such 
properties  with  the  exception  of  shrinkage  are  not  usually 
a  matter  of  importance  to  the  Inspector 

TESTS 

51.  Resistance  to  Abrasion  or  Wear,     (a)  Gravel.     No 
standard  method  for  making  an  abrasion  test  for  gravel  has 
been  generally  adopted.     When  specified,  however,  a  test 


42  Gravel,  Sand  and  Clay 

devised  by  A.  S.  Rea  is  usually  made  by  first  screening 
the  gravel  so  as  to  obtain  two  products,  the  one  passing  a 
2-inch  and  retained  on  a  1-inch  screen,  the  other  passing 
the  1-inch  and  retained  on  a  J-inch  screen.  Twenty-five 
hundred  grams  (5J  Ibs.)  of  each  size  is  then  placed  in  a  Deval 
Abrasion  machine  together  with  six  cast-iron  spheres,  each 
about  1.9  inches  in  diameter  and  weighing  approximately 
one  pound.  The  test  is  made  in  the  same  -manner  as  for 
rock  (§  28)  and  the  amount  of  material  which  after  test 
passes  a  iVmcn  gieve  is  expressed  as  per  cent  of  wear.  When 
the  material  has  a  specific  gravity  below  2.20  a  total  weight 
of  4000  instead  of  5000  grams  of  material  is  used.  Results 
reported  by  Rea  vary  from  3.3  per  cent  for  a  hard  mixed 
gravel  to  30  per  cent  wear  for  a  poor  sandstone  gravel. 

(6)  Sand.  An  abrasion  test  for  sand  is  less  frequently 
used,  but  the  following  method  devised  by  F.  L.  Roman  has 
been  employed  by  the  Illinois  State  Highway  Commission. 
Five  hundred  grams  (1.1  Ib.)  of  the  sand  which  has  been 
passed  through  a  J-inch  screen  and  retained  on  a  50-mesh 
sieve,  and  which  has  been  washed  free  of  clay  and  organic 
matter,  is  placed  in  a  Deval  Abrasion  Machine  together  with 
250  grams  (1.05  Ibs.)  of  J-inch  spherical  steel  shot.  The 
charge  is  subjected  to  200  revolutions  at  the  usual  rate  for 
rock  (§  28)  after  which  the  per  cent  of  material  passing  a 
100-mesh  sieve  is  reported  as  the  per  cent  of  wear.  Under 
such  a  test  pure  quartz  sand  may  show  as  low  as  0,2  and  a 
soft  limestone  sand  as  high  as  7.6  per  cent  of  wear. 

52.  Cementing  Value.     The  cementing  value  of  gravel, 
topsoil,  and  sand  clay  is   determined  in  the  same  manner 
as  for  rock  (§  31)  except  that  only  that  portion  of  the  prod- 
uct which  passes  a  J-inch  screen  is  tested. 

53.  Washing   and   Elutriation   Tests,     (a)  The   washing 
test  usually  precedes  the  determination  of  size  or  grading 
of  which  it  is  really  a  part.    For  gravel  a  dry  sample  of  the 
material  weighing  not  less  than  50  times  the  weight  of  the 
largest  size  stone  present  is  placed  in  a  shallow  pan,  covered 


Tests  43 

with  water,  and  thoroughly  agitated  for  15  seconds.  After 
15  seconds'  sedimentation  the  water  is  poured  off  through 
a  200-mesh  sieve  and  the  operation  repeated  until  the  wash 
water  is  approximately  clear.  The  washed  material,  together 
with  any  residue  retained  on  the  sieve,  is  then  dried  and 
weighed.  The  difference  between  this  and  the  original  weight 
is  calculated  and  reported  as  per  cent  removed  by  washing. 

(6)  For  sand  approximately  100  grams  of  the  olry  ma- 
terial, accurately  weighed,  is  placed  in  a  500-c.c.  (1  pt.) 
glass  beaker  about  three  quarters  full  of  water  and  agitated 
in  such  a  manner  that  no  whirling  results.  After  settling 
for  20  seconds  the  water  is  poured  off  through  a  200-mesh 
sieve  and  the  operation  repeated  until  the  wash  water  is 
approximately  clear.  The  washed  material,  together  with 
any  residue  retained  on  the  sieve,  is  then  dried  and  weighed. 
The  difference  between  this  and  the  original  weight  is  cal- 
culated and  reported  as  per  cent  removed  by  elutriation. 

54.  Size  or  Grading.     Size  or  grading  tests  may  be  made 
by  the  Inspector  (§  371)  as  well  as  by  the  Laboratory.    If  a 
washing  or  elutriation  test  is  required,  the  residue  is  passed 
through  such  screens  and  sieves  as   are  required  by  the 
specifications  and  the  results  expressed  on  the  basis  of  weight 
of  the  original  sample.     When  such  preliminary  tests  are 
not  required,   the  same  weight  of    dry  sample    is   passed 
directly  through  the  screens  and  sieves.     The  per  cent  by 
weight  retained  on  each  screen  or  sieve  but  passed  by  the 
one  with  next  largest  openings,  together  with  the  per  cent 
passing  the  screen  or  sieve  with  smallest  openings,  is  reported. 

55.  Washing  Test  and    Grading   01    Topsoil   and    Sand 
Clay.     This  test  is  usually  made   in    the   laboratory.     A 
500-gram  sample  of  the  dry  material  is  passed  through  a 
10-mesh  sieve  and  that  which  is  retained  is  weighed  and 
recorded  as  coarse  material.     Fifty  grams  of  the  material 
which  passes  the  sieve  is  then  placed  in  a  wide-mouth  bottle 
with  5  c.c.  of  dilute  ammonia  water  and  200  c.c.  of  water. 
The  bottle  is  stoppered  and  shaken  for  20  minutes,  after 


44  Gravel,  Sand  and  Clay 

which  the  sample  is  allowed  to  settle  for  8  minutes  and  the 
supernatent  liquid  poured  off.  The  process  is  repeated  until 
the  supernatent  liquid  is  clear,  after  which  the  sample  is 
dried  and  weighed  and  the  difference  in  weight  recorded  as 
clay.  The  dried  residue  is  next  passed  through  20-,  60-, 
100-,  and  200-mesh  sieves,  the  residue  retained  on  each  sieve 
being  weighed  and  recorded  as  sand.  That  portion  passing 
the  200-mesh  sieve  is  also  weighed  and  recorded  as  silt.  All 
weights  are  calculated  to  the  percentage  of  the  original 
sample  taken,  and  reported  on  that  basis  under  the  headings 
coarse  material,  sand,  silt  and  clay. 

56.  Specific  Gravity.     When  little  or  no  material  will  pass 
a  J-inch  screen,  specific  gravity  is  determined  in  the  same 
manner  as  for  rock  (§  33) .     In  other  cases  the  product  is 
separated  into  two  sizes  by  means  of  the  J-inch  screen  and 
the  specific  gravity  of  each  is  determined.     For  fine  aggre- 
gates, or  those  passing  the  J-inch  screen,  optional  methods  of 
the    American    Society    for    Testing    Materials,    Tentative 
Standard  Test  D  55-18  T  may  be  used.     In  brief  this  test 
consists  in  measuring  the  volume  of  liquid  displaced  in  a 
special  measuring  flask  by  a  known  weight  of  the  material. 
The  weight  in  grams  divided  by  the  displaced  volume  in 
cubic  centimeters  gives  the  specific  gravity  of  the  product. 

57.  Determination  of  Voids.    The  per  cent   of  voids  in 
gravel  or  sand  may  be  determined  in  the  same  manner  as 
for  broken  stone  (§  34) . 

58.  Mortar  Tensile  Strength  Test  for  Sand.     This  test 
is  frequently  required  of  sand  to  be  used  in  hydraulic  cement 
concrete  construction  and  is  preferably  made  with  the  same 
brand  of  accepted  cement  proposed  for  use  on  the  job. 
Briquettes  composed  of  three  parts  of  the  sand,  passing  a 
J-inch  laboratory  screen,  to  one  part  of  cement  are  made  in 
the  same  manner  and  of  as  nearly  the  same  consistency  as 
possible  as  ordinary  standard  mortar  briquettes  which  are 
prepared  at  the  same  time  for  the  purpose  of  comparison. 
These  briquettes  are  stored  and  tested  at  the  end  of  7  and 


Sampling  45 

28  days  in  the  same  manner  as  the  ordinary  mortar  test  for 
Portland  cement  (§81).  The  average  tensile  strength  in 
pounds  per  square  inch  for  at  least  three  briquettes  is  com- 
pared with  that  of  the  standard  mortar  briquettes,  the 
results  being  usually  expressed  as  strength  ratio  on  a  per- 
centage basis.  Thus,  if  the  sand  produces  a  tensile  strength 
the  same  as  the  standard  mortar,  its  strength  ratio  is  said  to 
be  100% 

SAMPLING 

59.  Time  and  Place   of   Sampling.    Samples   of    gravel 
and  sand  products  may  be  taken  at  any  time  prior  to  or 
during  their  use.    As  in  the  case  of  rock,  when  the  specifica- 
tions require  physical  properties  which  must  be  determined  by 
laboratory  test,  a  preliminary  sample  should  be  taken  from 
each  proposed  source  of  supply  at  least  two  weeks  before 
final  acceptance.    Preliminary  samples  may  be  taken  from 
the  bank  or  pit  where  the  material  occurs  or  from  the  dredg- 
ing plant  if  it  occurs  under  water.    Additional  samples  for 
size  or  grading  determinations  should  be  taken  after  screen 
ing,  if  screening  is  required,  from  bins,  cars,  scows  or  storage 
piles  on  the  job.    Frequent  samples  should  be  taken  and  tested 
on  the  job  by  the  Inspector  (§  371),  particularly  in  the  case 
of  mixed  products  or  when  grading  is  an  important  factor. 

60.  Methods  of  Sampling,     (a)  The   precautions  to  be 
taken  in  sampling  for  either  quality,  or  size  or  grading,  are 
essentially  the  same.    The  greatest  care  is  required  to  insure 
obtaining  samples  which  are  strictly  representative  of  the 
material  as  a  whole.    Samples  of  gravel  or  of  material  con- 
taining gravel  should  never  weigh  less  than  fifty  times  the 
weight  of  the  largest  fragment  present.    When  the  material 
will  all  pass  a  f-inch  screen  it  is  advisable  to   make  the 
weight  of  the  sample  about  ten  pounds.     The   minimum 
weight  of  sample  will  of  course  be  governed  by  the  quantity 
required  for  the  tests  to  which  it  will  be  subjected.    Thus, 
if  gravel  is  to  be  tested  for  resistance  to  abrasion,  the  sample 


46  Gravel,  Sand  and  Clay 

should  be  of  sufficient  size  to  produce  upon  screening  at 
least  six  pounds  each  of  material  passing  the  2-inch  and 
retained  on  the  1-inch  screen,  and  passing  the  1-inch  and 
retained  on  the  J-inch  screen.  By  special  direction  of  the 
Engineer  or  the  Laboratory  samples  of  gravel  and  sand  may 
be  required  of  sufficient  size  to  make  large  concrete  speci- 
mens for  compression  tests.  This  may  require  as  much  as 
two  cubic  feet  of  coarse  aggregate  and  one  cubic  foot  of 
fine  aggregate. 

(6)  When  sampling  from  a  pit  or  bank,  if  the  deposit  does 
not  appear  to  be  reasonably  uniform,  individual  samples 
from  a  number  of  different  points  may  be  necessary  to  show 
the  possible  range  in  quality  or  grading.  Otherwise  a  sample 
should  never  be  taken  from  a  single  portion  of  the  deposit, 
but  a  composite  sample  should  be  prepared  by  mixing 
samples  taken  at  different  points.  Care  should  be  taken  to 
exclude  all  dirt  or  extraneous  materials  which  do  not  form 
a  part  of  the  deposit  to  be  worked.  Samples  are  taken  from 
unopened  deposits  by  digging  test  holes  of  such  depth  as 
will  be  represented  by  the  first  working  face.  In  a  deposit 
which  has  been  partially  excavated  samples  should  be 
secured  from  working  faces  as  nearly  vertical  as  possible  by 
scraping  the  face  with  a  trowel  or  pick  for  its  entire  depth 
and  collecting  only  that  portion  so  removed. 

(c)  When  sampling  from  bins,  cars,  barges  or  storage 
piles  better  average  samples  may  be  obtained  when  the 
material  is  damp  than  when  perfectly  dry  because  of  the 
greater  tendency  of  perfectly  dry  particles  of  the  same  size 
to  segregate.  Composite  samples  should  invariably  be  pre- 
pared by  mixing  samples  taken  from  various  portions  of  the 
pile.  At  each  point  sampled  a  hole  should  be  dug  and  the 
sample  obtained  by  scraping  from  the  bottom  upward  on  a 
vertical  face.  When  sampling  a  number  of  cars  or  piles  of 
supposedly  the  same  product,  an  individual  composite 
sample  should  be  taken  from  each  car  or  pile  which  for  any 
reason  appears  to  be  different  from  the  others. 


CHAPTER  IV 

HYDRAULIC  CEMENT 
GENERAL  CHARACTERISTICS 

.61.  Classification.  There  are  many  classes  and  sub- 
classes of  hydraulic  cements,  but  only  a  few  are  of  interest 
in  highway  work.  In  fact,  it  may  be  said  that  only  one, 
namely,  Portland  cement,  is  extensively  used  in  highway 
construction.  The  principal  classes,  including  quicklime, 
which  is  closely  related  but  does  not  possess  hydraulic 
properties,  are  as  follows: 

(a)  Portland  cement. 
(6)  Natural  cement. 

(c)  Puzzolan  cement. 

(d)  Hydraulic  lime. 

(e)  Common  quicklime. 

62.  Manufacture.  Portland  cement  is  produced  by  burn- 
ing to  incipient  fusion  an  intimate  mixture  of  finely  ground 
calcareous  and  argillaceous  materials,  such  as  limestone  and 
clay,  consisting  of  approximately  three  parts  of  calcium 
carbonate  to  one  part  of  silica,  alumina  and  iron  oxide,  and 
afterwards  finely  pulverizing  the  clinker.  Natural  cement, 
called  Rosendale  cement  in  certain  sections  of  the  country, 
is  made  by  burning  at  low  heat  limestone  containing  an 
excess  of  clay  and  often  considerable  magnesia,  and  after- 
ward finely  pulverizing  the  resulting  product.  Puzzolan 
cement  consists  of  an  intimate  finely  pulverized  mechani- 
cal mixture  of  slaked  lime  with  blast  furnace  slag  or  volcanic 
scoria  of  suitable  composition,  the  first  mixture  often  being 

47 


48  Hydraulic  Cement 

called  slag  cement.  Hydraulic  lime  is  produced  by  burning 
limestone  which  contains  a  small  amount  of  clay  and  reduc- 
ing it  to  powdered  form  by  the  addition  of  just  sufficient 
water  to  slake  the  free  lime  which  is  present.  Common 
quicklime  is  produced  by  burning  fine  soft  limestone  to 
remove  carbon  dioxide,  and  is  usually  obtained  in  lumps. 
.When  just  sufficient  water  is  added  to  slake  it  to  a  powder, 
hydrated  lime  is  produced. 

63.  Properties.     All  of  the  true  hydraulic  cements  possess 
the  property  of  hardening  under  water,  and  when  mixed  to 
a  paste  with  water,  of  setting  up  to  a  stone-like  mass.    When 
used  as  a  binding  medium  for  other  materials  such  as  sand, 
gravel,  and  broken  stone  they,  therefore,  produce  a  mono- 
lith.    When  mixed  with  water  certain  reactions  take  place 
between  the  calcium,  alumina  and  silica  compounds  present 
and  new  and  more  stable  mineral  constituents  are  formed 
which  interlock  and  produce  an  artificial  stone.     Common 
quicklime,    however,   reacts  with  water    to    form    calcium 
hydrate,  and  its  hardening  is  largely  due  to  the  later  forma- 
tion  of   carbonate   of  lime  through  absorption  of   carbon 
dioxide  from  the  air.     Specifications  for  hydraulic  cements 
may   include   limitations  for   a   few   chemical   components 
which  are  believed  to  be  deleterious  in  excessive  amount, 
also   strength  requirements  and   certain   properties   having 
to    do    with    workability.      While    exhibiting    considerable 
compressive  and  tensile  strength,  hydraulic  cements  which 
have  set  do  not  exhibit  the  same  degree  of  hardness   and 
resistance  to  abrasion  possessed  by  the  more  resistant  types 
of  rock.    Their  toughness  may,  however,  run  fully  as  high. 

SPECIFICATIONS  FOR  PORTLAND   CEMENT 

64.  Standardization.     Among  the  materials  used  in  high- 
way construction  Portland  cement  is  the  only  one  of  which 
it  may  be  said  that  a  single  uniform  standard  specification 
has  been   generally  adopted.     This  material  is,   however, 


Specifications  for  Portland  Cement         49 

peculiar  in  the  fact  that  its  quality  may  be  considered  irre- 
spective of  the  class  of  work  in  which  it  is  used,  the  char- 
acter of  other  materials  which  are  to  be  associated  with  it, 
variations  in  the  raw  materials  from  which  it  is  made,  and 
the  effect  of  local  conditions,  such  as  traffic  and  climate, 
upon  its  usefulness.  The  present  standard,  which  is  briefed 
in  the  following  paragraphs,  has  been  adopted  by  the  United 
States  Government  and  the  American  Society  for  Testing 
Materials  (Standard  C  9-17)  and  is  the  result  of  a  joint 
conference  of  representatives  from  both  sources,  together 
with  representatives  of  the  American  Society  of  Civil 
Engineers. 

65.  Definition.     "  Portland    cement   is   the   product   ob- 
tained by  finely  pulverizing  clinker  produced  by  calcining 
to  incipient  fusion  an  intimate  and  properly  proportioned 
mixture  of  argillaceous  and   calcareous  materials,  with  no 
additions   subsequent   to   calcination  excepting  water   and 
calcined   or  uncalcined   gypsum." 

66.  Chemical    Properties.     "The    following    limits    shall 
not  be  exceeded: 

Loss  on  ignition 4.00  per  cent 

Insoluble  residue 0.85    "      " 

Sulphuric  anhydride  (S08) 2.00    "     " 

Magnesia  (MgO) 5.00    " 

67.  Physical  Properties,     (a)  Specific  Gravity.     "  The  spe- 
cific gravity  of  cement  shall  be  not  less  than  3.10  (3.07  for 
white  Portland  Cement)." 

(6)  Fineness.     "The    residue    on    a    standard    200-mesh 
sieve  shall  not  exceed  22  per  cent  by  weight." 

(c)  Soundness.      "A   pat   of   neat   cement   shall   remain 
firm  and  hard  and  show  no  signs  of  distortion,  cracking, 
checking  or  disintegration    in   the  steam  test   for  sound- 
ness." 

(d)  Time   of  Setting.      "The   cement   shall   not   develop 
initial  set  in  less  than  45  minutes  when  the  Vicat  needle  is 


50  Hydraulic  Cement 

used  or  60  minutes  when  the  Gilmore  needle  is  used.     Final 
.set  shall  be  attained  within  10  hours." 

(e)  Tensile  Strength.  "The  average  tensile  strength  in 
pounds  per  square  inch  of  not  less  than  three"  standard  mortar 
briquettes  composed  of  1  part  cement  and  3  parts  stand- 
ard sand  by  weight  shall  be  equal  to  or  higher  than  the 
following: 


Age  at  Test 

Storage  of  Briquettes 

Tensile 
Strength 

7  days 
28  days 

1  day  in  moist  air,    6  days  in  water 

1       (i       (i         ..           u     oy       a        (i         >.' 

200 
300 

"The  average  tensile  strength  at  28  days  shall  be  higher 
than  that  at  7  days." 

68.  Packages,  Marking  and  Storage,     (a)  "The  cement 
shall  be  delivered  in  suitable  bags  or  barrels  with  the  brand 
and  name  of  the  manufacturer  plainly  marked  thereon,  un- 
less shipped  in  bulk.     A  bag  shall  contain  94  pounds  net. 
A  barrel  shall  contain  376  pounds  net." 

(6)  "The  cement  shall  be  stored  in  such  manner  as  to 
permit  easy  access  for  proper  inspection  and  identification 
of  each  shipment,  and  in  a  suitable  weather-tight  building 
which  will  protect  the  cement  from  dampness." 

69.  Inspection.     "Every  facility  shall  be  provided   the 
purchaser  for  careful  sampling  and  inspection  at  either  the 
mill  or  the  site  of  the  work,  as  may  be  specified  by  the  pur- 
chaser.    At  least  10  days  from  the  time  of  sampling  shall 
be  allowed  for  the  completion  of  the  7-day  test,  and  at  least 
31  days  shall  be  allowed  for  the  completion  of  the  28-day 
test.     The  cement  shall  be  tested  in  accordance  with  the 
methods    hereinafter    prescribed.      The    28-day    test    shall 
be  waived  only  when  specifically  so  ordered." 

70.  Rejection.     "The  cement  may  be  rejected  if  it  fails 
to  meet  any  of  the  requirements  of  these  specifications. 
Cement  shall  not  be  rejected  on  account  of  failure  to  meet 


Specifications  for  Natural  Cement          51 

the  fineness  requirement  if  upon  retest  after  drying  at 
100°  C.  for  one  hour  it  meets  the  requirement.  Cement 
failing  to  meet  the  test  for  soundness  in  steam  may  be 
accepted  if  it  passes  a  retest  using  a  new  sample  any  time 
within  28  days  thereafter.  Packages  varying  more  than 
5  per  cent  from  the  specified  weight  may  be  rejected;  and 
if  the  average  weight  of  packages  in  any  shipment  as  shown 
by  weighing  50  packages  taken  at  random  is  less  than 
specified,  the  entire  shipment  may  be  rejected." 


SPECIFICATIONS  FOR  NATURAL  CEMENT 

71.  Standardization.     Specifications   for   natural   cement 
have  not  received  the  same  amount  of  attention  as  for 
Portland    cement.      However,    the    American    Society   for 
Testing  Materials  adopted  a  standard   (C  10-09)  in  1909 
and  its  Committee  C-l  later  recommended  that  until  re- 
vision the  new  methods  of  tests  for  Portland  cement  (C  9-17) 
be  applied  to  the  testing  of  natural  cement.     This  speci- 
fication is  substantially  as  follows: 

72.  Definition.     "This  term  shall  be  applied  to  the  finely 
pulverized    product   resulting   from   the   calcination   of   an 
argillaceous  limestone  at  a  temperature  only  sufficient  to 
drive  off  the  carbonic  acid  gas." 

73.  Physical    Properties,     (a)  Fineness.     It    shall    leave 
by  weight  a  residue  of  not  more  than  10  per  cent  on  the 
100-,  and  30  per  cent  on  the  200-mesh  sieve. 

(b)  Time  of  Setting.     "It  shall  not  develop  initial  set  in 
less  than   10  minutes"    (when   the  Vicat  needle  is  used) 
"and  shall  not  develop  hard  set  in  less  than  30  minutes,  or 
in  more  than  3  hours." 

(c)  Tensile  Strength.     "The  minimum  requirements  for 
tensile  strength  for  briquettes  1  square  inch  in  cross  section 
shall  be  as  shown  on  the  table  on  the  following  page,  and  the 
cement  shall  show  no  retrogression  in  strength  within  the 
periods  specified." 


52 


Hydraulic  Cement 


Age  at 
Test 

Storage  of 

Briquettes 

Tensile  Strength 
Lbs.  per  sq.  in. 

Neat 
Cement 

Standard 
1:3  Mortar 

24  hours 
7  days 
28  days 

24  hours  in  moist 

1  day  in  moist  air 

i     u     «      «        << 

air 
.    6  days  in  water 

27     "      "       " 

75 
150 
250 

'50 
125 

(d)  Constancy  of  Volume.  "Pats  of  neat  cement  about 
3  inches  in  diameter,  £  inch  thick  at  center,  tapering  to  a 
thin  edge,  shall  be  kept  in  moist  air  for  a  period  of  24  hours. 
A  pat  is  then  kept  in  air  at  normal  temperature;  another 
is  kept  in  water  maintained  as  near  70°  F.  as  practicable. 
These  pats  are  observed  at  intervals  for  at  least  28  days, 
and,  to  satisfactorily  pass  the  tests,  shall  remain  firm  and 
hard  and  show  no  signs  of  distortion,  checking,  cracking 
or  disintegrating." 

74.  Package,  Marking  and  Storage.  These  requirements 
are  essentially  the  same  as  for  Portland  cement  (§  68)  except 
that  it  is  specified  that  a  bag  of  natural  cement  shall  contain 
94  pounds  and  each  barrel  shall  contain  282  pounds. 


vluo 


CEMENT  TESTS 


75.  Chemical  Analysis.  In  the  standard  specifications 
for  Portland  cement  the  methods  of  chemical  analysis  are 
described  in  detail,  but  are  of  no  particular  interest  to  the 
highway  Inspector.  For  the  loss  on  ignition  test  a  permis- 
sible variation  of  0.25  is  allowed  and  all  results  in  excess  of 
the  specified  limit  but  within  the  permissible  variation  are 
reported  as  4  per  cent.  For  the  insoluble  residue  a  permis- 
sible variation  of  0.15  is  allowed  and  all  results  in  excess  of 
the  specified  limit  but  within  the  permissible  variation  are 
reported  as  0.85  per  cent.  In  like  manner  a  permissible 
variation  of  0.10  for  sulphuric  anhydride  and  0.4  for  magnesia 
are  allowed  and  all  results  in  excess  of  the  specified  limits 


Cement  Tests  53 

but  within  the  permissible  variations  are  reported  as  2  per 
cent  and  5  per  cent  respectively. 

76.  Specific    Gravity.    The    determination    of    specific 
gravity  is  made  with  a  standardized  Le  Chatelier  flask  and 
in  brief  consists  of   ascertaining  the  volume  of   water-free 
kerosene  displaced  by  64  grams  of  the  cement.    The  weight 
of  cement,  divided  by  the  number  of  cubic  centimeters  of 
kerosene  displaced,  gives  the  specific  gravity  of  the  cement. 
If  a  test  upon  the  cement  as  received  falls  below  3.10  for 
Portland  cement,  a  second  test  is  made  on  a  freshly  ignited 
sample. 

77.  Fineness.     The  determination  for  fineness  is  made 
by  agitating,  in  a  specified  manner,  50  grams  of  the  cement 
upon  the  proper  standard  sieve  and  continuing  the  agita- 
tion until  not  more  than  0.05  gram  passes  through  in  one 
minute.     The   residue  remaining  upon  the  sieve  is  then 
weighed  and  its  per  cent  of  the  original  sample  calculated. 
For  Portland  cement  a  permissible  variation  of  1  is  allowed 
and  all  results  in  excess  of  the  specified  limit  but  within 
the  permissible  variation  are  reported  as  22  per  cent. 

78.  Normal  Consistency.     The  per  cent  of  water  neces- 
sary to  mix  with  the  cement  to  produce  a  paste  of  so-called 
normal  consistency  is  ascertained  by  making  trial  mixes 
until  a  paste  is  found  which  upon  being  tested  with  the 
Vicat  needle  will  show  a  settlement  of  the  needle  of  10  milli- 
meters at  the  end  of  a  J-minute  period.    This  instrument 
consists  of  a  movable  rod  of  standard  weight  and  dimensions 
which  is  carried  in  a  frame  so  that  when  released  it  will  have 
a  downward  vertical  movement.     A  removable  needle  of 
standard  size  can  be  inserted  in  one  end  of  the  rod.     The 
sample  of  cement  paste  is  held  in  a  standard  rubber  ring  on 
a  glass  plate  below  the  needle,  which  at  the   beginning  of 
the  test  is  just  brought  into  contact  with  the  upper  surface 
of  the  paste.    The  per  cent  of  water  necessary  to  produce  a 
standard  1 : 3  cement  mortar  is  ascertained  from  a  table  of 
water    equivalents    for    standard    mortars    compared    with 


54  Hydraulic  Cement 

normal    cement    pastes    containing    various    per    cents   of 
water.  .v.i'j 

79.  Soundness.     This   test  is  made  by  first  preparing  a 
pat  of  specified  shape  and  dimensions,  from  paste  of  normal 
consistency  (§  78).    The  pat  is  made  upon  a  glass  plate  and 
stored  in  moist  air  for  24  hours,  after  which  it  is  placed  in 
an  atmosphere  of  steam  just  above  boiling  water  for  a 
period  of  5  hours.    The  pat  is  then  examined  for  distortion, 
cracking,  checking  or  disintegration. 

80.  Time  of  Setting,     (a)  When   determining  the  time 
of  setting  of  cement  a  paste  of  normal  consistency  (§  78) 
is  first  prepared.     The  test   itself  is  made  either  with  the 
Vicat  apparatus  (§  78)  or  Gilmore  needle.     In  both  cases 
the  paste  is  kept  in  moist  air  throughout  the  test. 

(6)  With  the  first-mentioned  instrument  the  time  of  ini- 
tial set  is  the  period  elapsing  between  the  time  when  nor- 
mal consistency  is  secured  and  the  time  when  the  needle 
operating  for  \  minute  ceases  to  pass  a  point  5  millimeters 
above  the  glass  plate  on  which  the  sample  rests.  The  time  of 
final  set  is  the  period  elapsing  between  the  time  when  normal 
consistency  is  secured  and  the  time  when  the  needle  does 
not  sink  visibly  into  the  paste. 

(c)  The  Gilmore  needles  are  two  weighted  wire  rods.  The 
needle  of  larger  diameter  carries  a  weight  of  J  pound  and 
that  of  smaller  diameter  carries  a  weight  of  1  pound.  In 
making  a  test,  one  of  the  needles  is  held  in  a  vertical  posi- 
tion and  applied  lightly  to  the  surface  of  the  cement  paste. 
Initial  set  is  obtained  when  the  paste  will  bear  the  weight 
of  the  |-pound  needle  without  appreciable  indentation. 
Final  set  is  obtained  when  in  like  manner  it  will  bear  the 
weight  of  the  1-pound  needle. 

81  o  Mortar  Tensile  Strength.  A  mortar  of  normal  con- 
sistency (§  78)  is  first  prepared  from  a  mixture  of  water  with 
one  part  by  weight  of  the  cement  to  three  parts  by  weight  of 
standard  quartz  sand  obtained  from  Ottawa,  Illinois.  This 
sand  has  been  sieved  to  pass  a  20-mesh  and  be  retained  on 


Measurement  55 

a  30-mesh  standard  sieve.  The  mortar  is  then  molded  into 
standard  shape  briquettes  with  a  minimum  cross  section  of 
one  square  inch  and  stored  for  24  hours  in  moist  air,  after 
which  the  briquettes  are  placed  under  water  until  ready  to 
be  tested.  At  the  end  of  6-and  27-day  periods  of  water 
immersion,  at  least  three  briquettes  are  tested  in  a  tension 
machine,  being  subjected  to  a  load  applied  continuously 
at  the  rate  of  600  pounds  per  minute.  At  each  period, 
the  loads  required  to  pull  each  of  the  briquettes  apart  are 
averaged  and  reported  as  tensile  strength,  in  pounds  per 
square  inch. 

82.  Tensile  Strength  Neat  Cement.    While  this  test  is 
not  at  present  specified  for  Portland  cement,  it  may  be  re- 
quired for  natural  cement.    It  is  made  in  exactly  the  same 
manner  as  described  for  mortar  (§  8.1)  except  that  the  bri- 
quettes are  made  from  cement  paste  of  normal  consistency 
and  one  set  of  briquettes  is  tested  after  twenty-four  hours' 
storage  in  moist  air  as  well  as  after  immersion  in  water  for 
the  additional  two  periods. 

MEASUREMENT 

83.  Basis  of  Purchase.     Hydraulic  cement  may  be  pur- 
chased directly  on  a  weight  basis,  but  it  is  usually  purchased 
by  the  bag  or  barrel  unit  with  the  weight  of  the  unit  speci- 
fied.   Inspection  of  quantity  delivered  or  used  should,  there- 
fore, be  checked  by  weight  (§  70)  as  well  as  by  count  of  the 
bags  or  barrels.    Counting  empty  sacks  is  not  a  safe  proce- 
dure unless  checked  by  counting  also  the  unused  material 
in  the  shipment  of  known  amount  from  which  the  used 
material  has  been  drawn. 

84.  Volume  and  Weight  Relations,    (a)  Experiments  have 
shown  that  freshly  sifted  Portland  cement  may  weigh  as  low 
as  80.3  Ib.  per  cubic  foot,  while  packed  cement  may  weigh 
as  high  as  123.2  Ib.  per  cubic  foot.    As  cement  is  commonly 
used  by  volume  proportion  in  construction  work,  it  is,  there- 


56  Hydraulic  Cement 

fore,  very  necessary  that  specifications  state  the  weight  per 
unit  volume  which  will  govern  its  use  in  the  work  specified. 
For  this  purpose  the  two  most  common  assumptions  are 
that  one  sack  of  94  pounds  will  represent  a  cubic  foot  or 
that  one  cubic  foot  will  weigh  100  pounds.  In  the  latter 
case  a  standard  barrel  would  represent  3.76  cu.  ft. 

(b)  The  voids  in  Portland  cement  are  of  no  practical 
interest  insofar  as  its  use  in  ordinary  mortar  or  concrete 
work  is  concerned.  This  is  because  of  the  fact  that  when 
acted  upon  by  water  chemical  reactions  take  place  which 
produce  entirely  different  material.  Cement  is,  however, 
sometimes  used  as  an  inert  filler  in  bituminous  concrete 
where  no  water  is  employed,  in  which  case  its  percentage  of 
voids  becomes  a  matter  of  interest.  Upon  the  assumption 
that  the  specific  gravity  of  cement  is  very  close  to  3.1  and 
considering  the  extremes  in  weight  mentioned  in  the  pre- 
ceding paragraph,  the  voids  in  loose  cement  may  be  as  high 
as  58  per  cent  and  in  packed  cement  as  low  as  36  per  cent. 
Forty  per  cent  of  voids  may  safely  be  assumed  for  cement 
when  used  as  an  inert  filler.  Upon  this  basis  a  cubic  foot 
of  cement  will  weigh  approximately  116  pounds. 


85.  Time  and  Place  of  Sampling.  Cement  should  be 
sampled  at  least  ten  days  in  advance  of  its  acceptance  or 
rejection,  when  such  is  decided  upon  the  basis  of  a  7  day 
test,  but  preferably  at  least  31  days  in  advance.  It  may 
be  sampled  either  at  point  of  manufacture  or  at  its  des- 
tination. If  it  is  necessary  to  use  it  promptly  upon  arrival 
at  its  destination,  arrangement  should  be  made  for  samp- 
ling at  the  factory.  Additional  samples  are  advisable  if  the 
cement  has  been  stored  for  long  periods  since  first  accepted 
or  if  for  any  reason  it  is  believed  to  have  deteriorated,  due 
to  imperfect  protection  from  the  weather  during  shipment 
or  storage. 


Sampling  57 

86.  Methods  of  Sampling,  (a)  Samples  taken  from  the 
factory  may  be  secured  from  the  conveyor  delivering  to 
the  bin,  from  the  bins  themselves  by  means  of  proper  sam- 
pling tubes,  or  from  the  bins  at  point  of  discharge.  Unless 
otherwise  directed,  only  composite  samples  prepared  from 
a  number  of  individual  samples  should  be  forwarded  to 
the  Laboratory.  In  no  case,  however,  should  a  single  com- 
posite sample  represent  over  200  barrels  or  an  individual 
sample  over  100  barrels.  When  sampling  from  the  con- 
veyors or  discharges,  small  samples  should  be  secured  at 
intervals  throughout  the  passage  of  each  200  barrels  and 
thoroughly  mixed  to  produce  the  composite  samples.  When 
sampling  from  the  bin  samples  are  secured  from  points  well 
distributed  over  the  face  of  the  bin,  and  whenever  practicable 
for  the  entire  depth  of  the  material,  not  to  exceed  10  feet. 
Sampling  tubes  inserted  horizontally  may  be  used  where 
the  construction  of  the  bin  permits. 

(6)  When  sampling  from  cars  or  warehouses  individual  or 
composite  samples  are  prepared  for  shipment  to  the  Labora- 
tory as  directed.  Composite  samples  should,  when  possible, 
be  prepared  from  samples  taken  from  one  sack  in  each  40 
sacks,  or  one  barrel  in  each  10  barrels,  in  as  many  different 
parts  of  the  car  or  storage  space  as  possible.  An  individual 
sample  should  represent  not  more  than  50  sacks.  In  no 
case  should  a  single  composite  sample  represent  over  200 
barrels,  and  in  lots  of  less,  than  one  car  load  the  sample 
should  represent  at  least  5  bags.  When  sampling,  each 
sample  from  bag  or  barrel  should  be  taken  from  surface  to 
center  and  each  sample  from  bulk  shipment  should  be 
obtained  from  top  to  bottom. 

(c)  Each  sample,  whether  individual  or  composite,  which 
is  forwarded  to  the  Laboratory  should  weigh  between  8  and 
10  pounds  and  be  shipped  in  an  air-tight  container. 


CHAPTER  V 

BITUMINOUS   MATERIALS 

GENERAL  CHARACTERISTICS 

87.  Composition.    From  the  standpoint  of  highway  engi- 
neering,   bituminous    materials    are    materials    containing 
bitumen  as   an   essential   constituent.     Without   confusing 
himself  with  the  rather  involved  technical   definition,  the 
Inspector  may  consider  bitumen  as  being  the  hydrocarbon 
compounds  constituting  the  whole  or  the  greater  part  of 
petroleum,   asphalt   and  tar  products,  which  will   dissolve 
in  carbon  disulphide.     Bitumen,  as  used  in  highway  work, 
may  exist  in  liquid,  semisolid,  or  solid  form,  but  if  semisolid 
or  solid  it  may  be  rendered  liquid  by  the  application  of  heat. 

88.  Classification.     Two    main    groups    of    bituminous 
materials    exist:     (1)     those    consisting    of    or    containing 
petroleum  or  asphalt  products,  and  (2)  those  consisting  of 
or  containing  tar  products.     Both  of  these  groups  may  be 
classified  according  to  their  principal  uses  as  follows: 

Surface  Treatment  of  Highways: 
Dust  Preventives 
Carpeting  Mediums 
Seal  Coating  Materials 

Incorporation  in  the  Highway  Structure: 
Bituminous  Cements 
Bituminous  Fillers 
Bituminous  Aggregates. 

In  additiofi,  certain  tar  products  are  used  as  impregnating 
materials  for  wood  block.     In  both  groups  the  consistency 

58 


General  Characteristics  59 

of  the  bitumen  may  run  from  very  fluid  to  almost  solid  for 
the  various  purposes  listed. 

89.  Manufacture,     (a)  The  desired  consistency  of  bitu- 
minous materials  is  usually  obtained  by  one  or  more  manu- 
facturing processes,  such  as  distillation,  oxidation  or  blow- 
ing, fluxing,  and  emulsification.    In  distillation,  two  classes 
of  products  are  formed,  distillates  and  residues.    The  former 
are  almost  always  relatively  thin  liquids  possessing  no  bind- 
ing qualities.    Residues,  on  the  other  hand,  run  from  liquids 
to  solids,  according  to  the  extent  of  distillation  or  amount 
of  distillate  removed.     Water  and  the  more  volatile  con- 
stituents  of   crude   petroleum   are   sometimes  removed   by 
distillation  and  sometimes  by  heating  the  material  in  a  coil 
of  pipe  so  that  pressure  is  developed.    The  hot  oil  is  then 
allowed  to  expand  suddenly  and  the  water  existing  as  steam 
leaves  without  producing   foaming.     This  process  is  called 
topping. 

(6)  By  blowing  air  through  certain  fluid  residues  at  a 
proper  temperature  they  may  be  converted  by  chemical 
action  and  without  material  distillation  into  semisolid  or 
solid  products.  Such  products  are  known  as  blown  asphalts. 
By  mixing  a  semisolid  or  solid  with  a  liquid  bituminous 
material  the  former  is  softened.  This  process,  known  as 
fluxing,  is  frequently  conducted  at  the  paving  plant  and  is 
subject  to  inspection.  Most  fluxes  are  fluid  residues,  but 
in  some  cases  distillates  are  employed,  and  the  resulting 
product  is  called  a  cut-back.  Emulsified  or  emulsifiable 
bituminous  materials  are  those  to  which  a  saponifying  agent 
or  soap  has  been  added  so  that  the}  may  be  mixed  with 
water  to  any  desired  extent  and  thus  be  rendered  more 
fluid. 

90.  Temperature    Control.     In    order    to    be    properly 
applied  or  used  in  highway  work  many  bituminous  materials 
must  be  made  temporarily  more  fluid  by  the  application  of 
heat.    The  heating  process  may  be  conducted  in  open  kettles, 
tank  cars,  or  tank  wagons,  and  when  fluxing  is  required, 


60  Bituminous  Materials 

prolonged  agitation  of  the  heated  material  is  necessary  as 
well.  In  some  cases  the  temperature  to  which  the  material 
must  be  raised  may  cause  loss  through  volatilization  of 
some  of  its  lighter  constituents,  particularly  if  agitation  is 
required,  with  the  result  that  if  cooled  the  material  will 
become  harder  or  more  solid  than  it  was  at  first.  Further-, 
more,  if  the  temperature  is  raised  too  high,  chemical  re- 
actions may  take  place  which  will  injure  or  ruin  the  product 
for  highway  purposes.  At  very  high  temperature,  the 
product  may  even  catch  fire  and  burn.  Proper  control  of 
temperature  during  use  is,  therefore,  a  vital  matter  which 
should  be  closely  observed  by  the  Inspector.  Specifications 
usually  place  a  maximum  temperature  limit  at  which  the 
material  may  be  heated  and  sometimes  state  that  all  material 
heated  above  such  temperature  shall  be  rejected.  In  addi- 
tion to  the  bituminous  material  proper,  it  may  also  be  neces- 
sary to  heat  broken  stone,  gravel  or  sand  with  which  it  is 
to  be  mixed.  In  such  cases,  just  as  much  necessity  exists 
for  proper  temperature  control  of  the  mineral  matter  as  for 
the  bituminous  material.  When  mixed  with  a  mineral 
aggregate,  the  bituminous  material  exists  in  relatively  thin 
films  surrounding  each  particle,  and  overheating  of  the 
aggregate  will  injure  the  bituminous  material  more  rapidly 
than  overheating  to  the  same  extent  in  a  kettle. 

91.  Effect  of  Water.  It  is  very  doubtful  if  the  presence 
of  water  in  most  bituminous  materials  before  use  results 
in  any  injury  to  the  material  itself.  With  few  exceptions, 
however,  bituminous  road  materials  are  free  from  water  as 
manufactured,  and  specifications  often  require  this.  The 
presence  of  even  a  very  small  amount  of  water  in  bitumi- 
nous materials  which  have  to  be  heated  may  seriously  inter- 
fere with  their  proper  use  or  application.  Thus,  a  few 
tenths  of  1  'per  cent  of  water  may  cause  the  product  to 
foam  almost  completely  out  of  a  kettle  when  heated  rapidly 
above  the  boiling  point  of  water,  and  considerable  time  may 
be  consumed  in  driving  off  the  water  in  order  to  heat  the 


General  Characteristics  61 

material  to  the  desired  temperature  without  foaming. 
Suitable  precautions  should,  therefore,  be  taken  to  prevent 
water  from  becoming  mixed  with  a  bituminous  material  or 
finding  its  way  into  the  heating  tank  or  kettle.  In  some 
cases,  such  as  shipment  of  material  in  a  tank  car  fitted  with 
leaky  steam  coils  for  heating  purposes,  it  may  be  necessary 
to  reject  bituminous  material  containing  water  owing  to 
the  impossibility  of  heating  it  to  the  temperature  desired 
for  use.  Water  which  has  accumulated  on  the  surface  of 
hard  bituminous  materials,  as  in  the  heads  of  barrels  stored 
in  the  open,  may  often  be  removed  with  a  large  sponge 
before  the  material  is  introduced  into  the  kettle. 

92.  Transportation  and  Storage.  Large  quantities  of 
fluid  bituminous  materials  are  ordinarily  shipped  to  the 
consumer  in  tank  cars  of  from  4000  to  12,000  gallons  capa- 
city. These  tank  cars  are,  as  a  rule,  equipped  with  steam 
coils  which  may  be  connected  from  the  outside  with  the 
boiler  of  a  road  roller  or  tractor,  in  case  it  is  necessary  or 
desirable  to  heat  the  material  before  unloading.  Semisolid 
mateiials  are  also  sometimes  shipped  in  tank  cars,  in  which 
case  it  is  very  important  that  the  coils  be  so  designed  and 
placed  as  to  insure  efficient  heating  of  the  entire  contents. 
A  very  large  proportion  of  the  semisolid  and  solid  materials 
is,  however,  shipped  in  barrels  or  drums.  For  the  harder 
grades  which  require  fluxing,  open-head  slack  barrels  are 
often  used.  These  barrels  are  clayed  on  the  inside  so  that, 
after  cutting  the  hoops,  the  staves  may  be  stripped  from 
the  material  with  little  or  no  waste.  Slack  barrels  hold 
from  300  to  400  pounds  of  material,  depending  largely  upon 
its  specific  gravity.  In  some  cases,  slack  barrels  may  be 
double-headed,  but  in  any  event  they  should  be  stored  on 
end  or  otherwise  they  are  apt  to  cave  in,  due  to  unequalized 
strains  produced  by  the  slow  flow  or  deformation  of  the 
bituminous  material  within.  Double-head  tight  barrels  of 
approximately  50  gallons'  capacity,  but  sometimes  varying 
from  40  to  60  gallons'  capacity,  are  largely  used  for  semi- 


62  Bituminous  Materials 

solid  and  viscous  bituminous  materials.  They  are  much 
stouter  than  the  slack  barrel,  but  when  stored  for  long 
periods  should  be  placed  on  end.  Thin  sheet  metal  drums 
are  also  used  to  a  considerable  extent  in  place  of  barrels  for 
the  transportation  of  semisolid  bituminous  materials. 
These  drums  are  made  with  both  single  and  double  heads. 
They  are  of  light  weight  and  hold  from  375  to  525  pounds  of 
material.  They  are  readily  dented  and  sometimes  punc- 
tured during  loading  or  unloading  and  require  careful  hand- 
ling, as  punctures  are  practically  impossible  to  repair  and 
May  result  in  the  loss  of  considerable  material  during  storage. 
They  cannot  be  stacked  without  slowly  pressing  out  of  shape 
and  bursting. 

PETROLEUM  AND   ASPHALT  PRODUCTS 

93.  Types  of  Petroleum.  There  are  two  distinct  types 
of  crude  petroleum:  the  paraffin  with  a  greasy  base;  and 
the  asphaltic  with  a  sticky  or  adhesive  base.  From  a  chemi- 
cal standpoint,  there  is  also  an  intermediate  type  known  as 
semiasphaltic.  Paraffin  petroleums  are  of  interest  from 
the  standpoint  of  highway  engineering  only  as  dust  pre- 
ventives or  for  the  manufacture,  by  distillation,  of  residual 
fluxes  which  are  used  to  soften  asphalts  to  any  desired  con- 
sistency. Crude  asphaltic  petroleums  are  sometimes  used 
directly  in  the  surface  treatment  of  roads,  but  are  more 
frequently  distilled  to  proper  consistency  for  one  of  the  uses 
listed  (§  88) .  The  oxidation  process  known  as  blowing  is 
frequently  employed  in  connection  with  distillation  to  pro- 
duce road  and  paving  materials  from  semiasphaltic  petro- 
leums. Blowing  is  also  used  to  some  extent  in  refining 
asphaltic  petroleums  when  it  is  desired  to  produce  residues 
the  consistency .  of  which  is  affected  comparatively  little  by 
temperature  changes  and  where  high  ductility  is  not  con- 
sidered an  important  characteristic. 

The  following  table  shows  the  source  of  the  more  common 


Petroleum  and  Asphalt  Products  63 

petroleums  used  in  the  United  States,   and  their  residual 
products  which  are  of  interest  in  highway  work: 

PETROLEUM  PRODUCTS 


Crude  Material 

Refining 
'    Process 

Refined 
Product 

Use 

Paraffin  Petroleum 
Pennsylvania 
Ohio,  Ind.  or  Lima 

Distillation 

Residual  oil 

Flux 

Semiasphaltic  Petroleum 
Mid-Continent 
Texas 
SouUiern  Illinois 

1.  Distillation 

2.  Distillation 
&  Blowing 

Residual  oil 
Blown  oil 

Dust  preventive 
Carpeting  medium 
,Flux 
'  Seal  coat  material 
Asphalt  cement    + 
Joint  filler 

Asphaltic  Petroleum 
California 

Mexican 
Trinidad 

1.  Topping 
2.  Distillation 

3.   Distillation 
&  Blowing 

Topped  oil 

/  Residual  oil 
(  Asphalt 

Blown  asphalt 

Carpeting  medium 
/  Carpeting  medium 
1  Flux 
Seal  coat  material 
Asphalt  cement 
Seal  coat  material 
Asphalt  cement 
Joint  filler 

94.  Petroleum  Distillates.     Petroleum  distillates  are  rela- 
tively thin  fluids  running  from  almost  colorless  to  opaque 
reddish  brown.    The  more  volatile  distillates  which  contain 
an  appreciable  quantity  of  gasoline  or  naphtha  are  some- 
times used  as  fluxes  for  asphalts  in  the  manufacture  of  cut- 
back products.    The  heavier,  more  viscous  and  nonvolatile 
distillates  resemble  inferior  lubricating  oil  and  are  useful 
only  as  dust  layers,  for  which  purpose  they  may  be  applied 
cold.    They  seldom,  if  ever,  exceed  0.920  specific  gravity  or 
12.0  specific  viscosity  (§  123)  at  25°  C.  (77°  F.). 

95.  Liquid  Petroleum  Residues,     (a)  Liquid   petroleum 
residues  are  dark  brown  to  black  products  varying  in  con- 
sistency from  thin  fluid  to  almost  semisolid,  according  to  the 
character  of  the  original  oil  and  the  extent  to  which  it  has 
been  distilled.     Those  produced  from  paraffin  petroleums 
are  greasy  and  are  of  value  only  as  fluxes  for  asphalts.    The 
thin  fluid  semiasphaltic  residues  are  sometimes  used  as  dust 


64  Bituminous  Materials 

preventives,  while  the  more  viscous  and  less  volatile  are 
used  as  fluxes  and  to  some  extent  as  carpeting  mediums, 
although  they  are  frequently  deficient  in  cementing  quali- 
ties. The  asphaltic  residues  produced  by  topping  or  dis- 
tillation are  usually  quite  viscous  and  possess  or  develop 
considerable  binding  value.  They  are  used  as  carpeting 
mediums  and,  if  free  from  volatile  constituents,  as  fluxes 
for  the  hard  asphalts. 

'(b)  Residual  carpeting  mediums  for  cold  application  are 
seldom  less  than  0.93  or  more  than  0.97  specific  gravity. 
They  usually  show  a  specific  viscosity  (§  123)  of  from  80 
to  120  at  25°  C.  (77°  F.).  The  better  grades  for  hot  appli- 
cation have  a  specific  gravity  of  over  0.98.  They  shew  a 
float  test  of  over  60  seconds  at  32°  C.  (90°  F.),  but  a  specific 
viscosity  at  100°  C.  (212°  F.)  of  less  than  60. 

(c)  Residual  fluxes  vary  in  specific  gravity  usually  be- 
tween the  limits  of  0.92  for  paraffin  residues  and  1.02  for 
asphaltic.  Their  consistency  varies  greatly  but,  in  general, 
increases  with  their  specific  gravity.  They  should  possess 
an  open  flash  point  higher  than  the  temperature  to  be  used 
in  fluxing  and  should  lose  little  or  no  volatile  material  at  that 
temperature. 

96.  Asphalts  and  Asphalt  Cements,  (a)  Asphalts  and 
asphalt  cements  are  solid  and  semisolid  products  produced 
from  petroleum  by  processes  of  distillation  or  blowing,  or 
similar  products  existing  as  such  in  natural  deposits.  Those 
properly  ,  produced  from  petroleum  are  practically  pure 
bitumen,  while  the  native  asphalts  sometimes  carry  a  high 
percentage  of  mineral  and  organic  impurities.  Petroleum 
asphalts,  often  called  oil  asphalts,  are  usually  manufactured 
so  as  to  be  of  suitable  consistency  for  use.  When  this  is  so, 
they  are  called  asphalt  cement  or  A.  C.  If  too  hard  for  use, 
they  are  called  refined  asphalt  or  R.  A.  Native  asphalts  are 
usually  too  hard  for  direct  use  in  highway  work  and,  after 
refining  to  produce  an  R.  A.,  must  be  combined  in  suitable 
proportions  with  a  flux  to  produce  an  A.  C.  of  proper  con- 


Petroleum  and  Asphalt  Products  65 

sistency  for  use.  The  bitumen  of  a  fluxed  native  asphalt 
may  be  very  similar  if  not  identical  to  that  of  an  asphalt 
cement  of  the  same  consistency  produced  by  the  distilla- 
tion of  an  asphaltic  petroleum.  Blown  asphalts,  however, 
are  considerably  different  in  their  physical  properties,  the 
most  marked  difference  being  a  much  higher  melting  point 
for  a  given  penetration  and  a  much  lower  ductility  and  lower 
specific  gravity.  Asphalts  and  asphalt  cements  range  in 
penetration  (§  125)  at  normal  temperature,  usually  between 
the  limits  of  0  and  200.  If  an  asphalt  shows  a  lower  pene- 
tration than  40  it  almost  invariably  has  to  be  fluxed  before 
use. 

(6)  Petroleum  asphalts  and  asphalt  cements  most  com- 
monly used  in  the  United  States  and  which  are  manufactured 
by  distillation  without  blowing  are  produced  from  Cali- 
fornia and  Mexican  petroleums  and  sometimes  from  mix- 
tures of  one  of  these  oils  with  a  semiasphaltic  oil.  To  pro- 
duce asphalt  from  the  semiasphaltic  petroleums  such  as 
the  Texas,  Mid-continent  and  Southern  Illinois  oils,  usually 
necessitates  blowing  as  well  as  distillation,  although  sub- 
jecting the  oil  to  a  special  preliminary  cracking  process, 
may  make  blowing  unnecessary.  In  certain  instances, 
asphalts  are  manufactured  from  the  sludge  obtained  by 
treating  petroleum  distillates  with  sulphuric  acid,  in  which 
case  they  are  known  as  sludge  asphalts. 

(c)  The  most  common  native  asphalts  used  in  this  coun- 
try are  obtained  from  the  Island  of  Trinidad  and  from  Ber- 
mudez,  both  in  Venezuela.  Solid  brittle  bitumens,  known 
as  Gilsonite  and  Grahamite,  which  occur  in  different  parts 
of  the  United  States,  are  also  used  to  some  extent,  par- 
ticularly in  combination  with  oils  or  asphalts  which  have 
been  blown.  The  native  asphalts,  Trinidad  and  Bermudez, 
have  to  be  refined  before  they  are  fluxed  to  produce  asphalt 
cements.  The  refining  process  consists  in  heating  them  so 
as  to  remove  water,  gas  and  some  of  the  coarse  organic  and 
mineral  impurities.  In  both  asphalts,  an  appreciable 


66  Bituminous  Materials 

amount  of  non-bituminous  material  remains  after  refining, 
but  the  refined  product  as  marketed  is  of  quite  uniform 
composition.  Refined  Bermudez  asphalt  contains  approxi- 
mately 94  per  cent  bitumen  and  refined  Trinidad  asphalt 
56  per  cent  bitumen.  It  is  evident  that  asphalt  cements 
produced  by  fluxing  these  refined  products  will  vary  in  their 
bitumen  content  according  .to  the  amount  of  flux,  consisting 
of  practically  pure  bitumen,  which  is  used. 

97.  Asphalt   Fillers.     There    are    two    types    of    asphalt 
fillers  used  for  filling  joints  in  pavements,  the  poured  joint 
filler,    and   the   prepared    or   premolded   joint   filler.     The 
former  is  really  an  asphalt  cement,  usually  produced  by  the 
blowing  process.     It  may  be  a  straight  petroleum  product 
or  one  containing  Gilsonite  or  Grahamite.    The  premolded 
fillers,    sometimes   called  expansion  joints,  are  bituminous 
strips  of  suitable  width  and  thickness.    They  may  be  of  the 
same  composition  as  the  poured  joint  filler  or  a  mixture  of 
asphalt   cement  with  such  substances   as  limestone   dust, 
silica,  or  shoddy  dust.    Sometimes  they  are  reinforced  with 
fa*bric  and  sometimes  they  consist  of  one  or  more  layers  of 
fabric  or  felt  saturated  with  asphalt.     Prepared  expansion 
joints  reinforced  or  armored  with  metal  are  also  manufactured. 

98.  Cut-back    Asphalts.     Cut-back  asphalts  or    asphalt 
cements  are  those  which  have  been  fluxed  with  a  distillate, 
usually  of  a  volatile  nature.     The  purpose  of  the  distillate 
is  to  temporarily  soften  the  asphalt  cement  which  has  the 
ultimate  desired  consistency  but  which-  cannot  be  readily 
used  in  its  original  state  in  the  type  of  treatment  or  construc- 
tion specified.    Such  products  should,  after  use,  rapidly  lose 
the  distillate  flux  by  volatilization  and  return  to  approxi- 
mately the  same  consistency  as  the  original  asphalt  cement. 
Thus,  if  it  is  desired  to  apply,  without  heating,  an  asphalt 
cement  to  a  road  surface,  the  asphalt  cement  may  be  fluxed 
with  a  volatile  distillate  until  sufficiently  fluid  to  apply  cold. 

99.  Emulsions  and  Emulsifying  Oils.    Petroleum  or  as- 
phalt products  are  ordinarily  insoluble  in  water.    They  may, 


Petroleum  and  Asphalt  Products  67 

however,  be  made  miscible  with  water  by  first  mixing  them 
with  soap  or  soap-forming  constituents.  Such  products 
can  then  be  brought  to  any  desired  degree  of  fluidity  by  the 
addition  of  water.  The  emulsifying  agents  commonly  em- 
ployed are  oleic  acid  or  cotton  seed  oil,  together  with  caustic 
soda,  potash,  or  ammonia.  In  addition,  carbolic  acid,  pine 
oil,  and  various  other  materials  are  sometimes  used.  The 
manufacture  of  an  emulsifiable  asphalt  is  often  a  difficult 
matter,  resulting  in  a  product  of  rather  unstable  equilibrium. 
If  this  equilibrium  is  once  destroyed,  the  product  is  rendered 
unemulsifiable  without  the  application  of  heat.  This  equilib- 
rium is  usually  destroyed  when  the  material  is  forced  into 
intimate  contact  with  stone,  sand,  gravel,  etc.  After  appli- 
cation to  a  road,  therefore,  the  material  is  not  susceptible 
to  removal  by  the  action  of  water. 

100.  Rock  Asphalt,  (a)  Rock  asphalt  is  limestone  or 
sandstone  naturally  impregnated  with  asphalt.  It  is  mined 
or  quarried  from  natural  deposits  by  methods  similar  to 
those  employed  in  rock  quarrying.  It  is  then  usually 
crushed  in  roll  or  hammer  crushers,  after,  which  further 
treatment  may  be  required  to  make  it  suitable  for  highway 
purposes,  where  it  is  used  directly  as  a  paving  material. 
Thus,  in  order  to  secure  the  proper  amount  of  asphalt  or 
bitumen  it  may  be  necessary  to  mix  two  or  more  grades  of 
rock  asphalt  containing  different  percentages  of  bitumen. 
It  may  even  be  necessary  to  add  more  asphalt  or  to  soften, 
that  already  present  by  the  addition  of  a  suitable  amount 
of  flux. 

(6)  Bituminous  limestone  may  be  of  a  semi-crystalline, 
conglomerate,  or  chalky  nature.  The  purer  carbonate 
rocks  crush  down  to  a  fine  powder,  each  particle  of  which 
appears  to  be  impregnated  with  bitumen.  Under  compres- 
sion, especially  at  an  elevated  temperature,  the  better  grades 
congeal  to  form  a  dense  tough  mastic.  They  occur  in  various 
parts  of  the  world,  but  the  domestic  deposits  only  are  of 
particular  interest  as  paving  materials  in  this  country.  The 


68  Bituminous  Materials 

best  known  of  these  occurs  in  Uvalde  County,  Texas,  as  a 
shell  limestone  or  conglomerate  impregnated  with  hard 
asphalt. 

(c)  In  bituminous  sandstones,  while  the  bitumen  per- 
meates the  natural  rock,  it  appears  to  coat  the  mineral  par- 
ticles rather  than  to  impregnate  them.  In  their  preparation 
for  use  the  sand  grains  are  not  necessarily  crushed  to  pro- 
duce a  mastic  with  the  bitumen,  but  may  be  merely  broken 
down  or  partly  separated.  A  prepared  bituminous  sand- 
stone may,  therefore,  have  the  general  appearance  of  a 
sheet  asphalt  paving  mixture,  although  the  mineral  particles 
are  seldom  as  well  graded.  A  deposit  occurring  in  Kentucky 
and  known  as  Kentucky  rock  asphalt  has  probably  been 
most  widely  used  in  this  country,  although  bituminous  sand- 
stones are  found  in  various  other  portions  of  the  United 
States,  and  certain  deposits  occurring  in  California  have 
also  been  used  in  paving  work. 
en  inlimig  sbofljtwi  v<i  a1i^<Kjob  f&iuttiri  arm'!  l»irn:u<> 

TAR  PRODUCTS 

•lomnji    d-nit//  /lyjifi    .  -io   iioi  m   iKMlxiT'-; 

101.  Types  of  Tar.  (a)  There  are  two  principal  types 
of  tar  of  interest  in  highway  engineering,  —  coal  tars  and 
water  gas  tars.  The  former,  as  their  name  implies,  are 
derived  from  coal.  They  are  incidentally  produced  as 
distillates  in  the  manufacture  of  gas  or  coke  by  the  destruc- 
tive distillation  of  bituminous  coal.  According  to  the  main 
object  of  the  process  which  involves  different  types  of  plant 
apparatus  and  largely  influences  the  character  of  the  tar, 
coal  tars  may  be  subdivided  into  two  groups,  gas-house  coal 
tars  and  coke-oven  tars.  Water  gas  tars  are  derived  from 
petroleum  products  by  a  process  of  destructive  distillation 
in  the  manufacture  of  carburretted  water  gas.  While  their 
origin  is  entirely  different,  they  closely  resemble  coal  tars, 
particularly  when  refined  for  use  in  highway  work.  Crude 
tars  are  sometimes  used  directly  in  the  surface  treatment  of 
roads,  but  are  usually  distilled  to  suitable  consistency.  All 


Tar  Products  69 

yield  semisolid  or  solid  pitches  if  distilled  to  a  sufficient  extent 
and,  therefore,  any  desired  consistency  of  the  sticky  tar 
residuum  or  refined  tar  may  be  obtained  by  distillation  only. 
The  blowing  process  is  also  sometimes  employed,  particularly 
in  the  manufacture  of  fillers. 

(6)  Both  physically  and  chemically,  tar  products  are 
quite  different  from  petroleum  and  asphalt  products  of  the 
same  consistency.  They  are  much  more  susceptible  to  tem- 
perature changes  than  the  latter  and  tend  to  harden  more 
rapidly  when  exposed  to  atmospheric  conditions.  These 
relative  properties  offer  certain  advantages  and  disadvan- 
tages which  are  of  considerable  interest  in  highway  engi- 
neering. Tar  products  are  used  as  dust  preventives,  carpet- 
ing mediums,  seal-coating  materials,  bituminous  cements, 
fillers,  and  also  as  impregnating  materials  for  wood  block. 
Owing  to  their  very  pronounced  susceptibility  to  tempera- 
ture changes,  tar  cements  are  not  well  adapted  for  and  are 
seldom  used  in  the  construction  of  fine  aggregate  bituminous 
concrete  highways. 

(c)  Tars  contain  a  widely  varying  percentage  of  free 
carbon  which  may  be  considered  as  an  inert  impurity  exist- 
ing in  the  form  of  finely  divided  soot.  This  material  is  sus- 
pended quite  uniformly  throughout  the  tar  and  is  insoluble 
in  carbon  disulphide  (§  133).  In  water-gas  tars  it  is  present 
to  a  very  limited  extent,  sometimes  amounting  to  but  a 
few  tenths  of  1  per  cent,  while  in  gas-house  coal  tars  it  may 
amount  to  30  per  cent  or  more:  Coke-oven  tars  usually 
carry  a  smaller  amount,  but  seldom  less  than  3  per  cent.  As 
free  carbon  is  nonvolatile,  it.  always  remains  in  the  residue 
of  a  tar  subjected  to  distillation  and  its  percentage  of  such 
residue,  therefore,  becomes  higher  as  the  percentage  of  dis- 
tillate removed  increases  during  distillation.  The  amount 
of  free  carbon  in  a  refined  tar  is  often  controlled  by 
blending  two  or  more  crude  tars,  which  contain  different 
percentages  of  free  carbon,  before  the  process  of  distillation 
is  commenced. 


70  Bituminous  Materials 

102.  Liquid  Refined  Tars.    Liquid  refined  tars  are  either 
tar  residues  or  mixtures  of  such  residues  with  a  smaller 
amount  of  crude  tar  or  tar  distillates.     They  are  black  in 
color  and  usually  have  a  strong  odor  of  tar  oils  and  naph- 
thalene.    They  vary  in  consistency  from  those  which  are 
sufficiently  fluid  to  apply  cold  to  those  which  require  heat- 
ing before  application.     They  are  used  to  some  extent  as 
dust   layers   but   more   frequently   as   carpeting   mediums. 
Those  which  are  viscous  possess  considerable  binding  power 
and  even  the  thin  fluids  rapidly  develop  binding  qualities 
after  application.    Those  which  are  to  be  applied  cold  often 
contain  a  small  amount  of  water  which  materially  reduces 
their  viscosity.     A  high  percentage  of  free  carbon  is  con- 
sidered undesirable,  as  this  material  tends  to  interfere  with 
absorption  of  the  tar  proper  by  the  road  surface.     The 
specific  gravity  of  liquid  refined  tars  varies  greatly,  depend- 
ing upon  their  consistency  and  the  amount  of  free  carbon 
present.     It  is,   however,   almost  invariably  greater  than 
1.100.     This  fact  alone  may  serve  to  differentiate  liquid 
refined  tars  from  liquid  petroleum  residues,  although  their 
characteristic  odor  is  usually  sufficient  for  this  purpose. 

103.  Semisolid  Refined  Tars,     (a)  The  semisolid  refined 
tars  are  usually  very  viscous  tar  residues  intended  primarily 
to  serve  as  bituminous  cements  in  the  road  structure  or  as 
seal-coating  materials.    Because  of  their  tendency  to  harden 
with   age   as   well   as   their   susceptibility   to   temperature 
changes  or  tendency  to  become  brittle  in  cold  weather,  they 
are  ordinarily  much   softer  than   asphalt  cements  manu- 
factured for  the  same  purpose.     In  fact,  they  are  so  soft 
that  their  consistency  is  seldom  determined  by  the  pene- 
tration test  (§  125),  the  float  test  (§  124)  being  used  for 
this  purpose.     They  have  a  much  higher  specific  gravity 
than  the  asphalts,  unless  the  latter  contain  a  considerable 
amount  of  mineral  matter,  as  in  the  case  of  Trinidad  asphalt. 
Their  specific  gravity,   depending  largely  upon  their  free 
carbon  content,  is  seldom  less  than  1.15  or  greater  than 


Measurement  71 

1.30.  When  used  in  bituminous  concrete,  the  free  carbon 
present  should  be  calculated  as  filler  rather  than  as 
bitumen. 

(6)  Sometimes  the  heavy  tar  residues  are  cut  back  with 
a  volatile  distillate  to  produce  a  material  for  maintenance 
by  cold  patching.  Such  products  are  commonly  known  as 
cold  patch  tars. 

104.  Pitch  Fillers.     Poured  joint  fillers  are  manufactured 
from  tars  by  distilling  and  blowing  the  residue  to  the  desired 
melting   point.     They   are   often   quite   hard   and   brittle, 
contain  a  high  percentage  of  free  carbon,  show  a  high  specific 
gravity  and  a  melting  point  of  45°  C.  (113°F.)  or  higher. 
They  are  much  more  susceptible  to  temperature  changes 
than  are  the  blown  petroleum  or  asphalt  products  prepared 
for  the  same  purpose.     The  prepared  tar  expansion  joints 
consist  of  one  or  more  layers  of  fabric,  felt  or  porous  paper 
saturated  with  refined  tar. 

105.  Creosoting  Oils.     Creosoting  oils  originally  included 
only  certain  distillates  of  coal  tar  rich  in  oxygenated  hydro- 
carbons known  as  cresols.     The  term  is  now  commonly 
applied  not  only  to  the  creosote  distillates  of  coal  tars  but 
also  to  other  tar  products  which  are  used  to  impregnate 
wood.     Creosoting  oils  may  be  divided  into  two  general 
classes,  heavy  distillates  of  coal  tars  and  water  gas  tars,  and 
residual  tars  or   oils   containing  tar  residues.     The   latter 
class  may  be  very  fluid  refined  water-gas  or  coke-oven  tars 
or  mixtures  of  refined  tars  with  tar  distillates.     Petroleum 
products  are  seldom  used  as  wood  preservatives. 

MEASUREMENT 

106.  Weight    Basis    (a)  The    harder    asphalt    cements, 
refined  asphalts  and  tar  pitches  are  commonly  purchased 
and,  therefore,  measured  by  weight,  and  all  materials  used 
in  bituminous  mixtures  are  commonly  measured  on  a  weight 
basis.    Because  of  considerable  difference  in  specific  gravity 


72  Bituminous  Materials 

as  well  as  the  presence  of  impurities  the  weight  of  a  bitu- 
minous material  does  not  represent  a  constant  which  can 
necessarily  be  taken  by  the  Inspector  without  qualification. 
When  purchase  is  made  by  weight  in  tank  car  lots,  freight 
weights  are  usually  accepted  as  a  basis  for  payment.  If, 
however,  shipment  is  made  in  barrels  or  drums,  the  weight 
of  such  containers  should  be  ascertained  and  deducted  from 
the  gross  weight  unless  purchase  is  made  and  clearly  under- 
stood to  be  upon  a  gross  weight  basis. 

(6)  The  aggregate  weight  of  containers  often  represents 
an  appreciable  percentage  of  the  gross  weight  of  bituminous 
materials.  Thus  slack  barrels  weighing  20  pounds  and 
each  holding  300  pounds  of  bituminous  materials  will  con- 
stitute over  6  per  cent  of  the  gross  weight  and  amount  to 
125  pounds  per  gross  ton.  Double-head  tight  barrels  may 
weigh  from  60  to  70  pounds  each  and  frequently  approxi- 
mate 15  per  cent  of  the  gross  weight  of  a  shipment.  Thin 
sheet  metal  drums  are  lighter  but  will  affect  the  net  weight 
to  some  extent. 

(c)  Sometimes  purchase  is  made  upon  the  basis  of  actual 
weight  of  bitumen  delivered  and  when  bituminous  materials, 
containing  an  appreciable  amount  of  impurities,  are  involved, 
recourse  must  be  had  to  laboratory  test  reports  in  estimating 
the  actual  weight  of  bitumen  represented.  This  is  a  very 
necessary  basis  for  estimating  the  percentage  of  bituminous 
material  to  be  used  in  bituminous  mixtures,  for  it  is  evident 
that  the  serviceability  of  such  mixtures  will  largely  depend 
upon  the  presence  of  the  proper  amount  of  bitumen,  which 
is  the  active  binding  material.  It  is  also  a  very  reasonable 
basis  of  purchase,  as  it  is  evident  that  a  ton  of  asphalt  con- 
taining 100  per  cent  bitumen  will  be  the  approximate 
equivalent  of  1.5  tons  of  asphalt  containing  35  per  cent  of 
mineral  matter  or  other  impurities.  The  specific  gravity  of 
a  bituminous  material  may  also  play  an  important  part  in 
the  estimate  of  quantities,  but  this  can  best  be  considered 
under  the  volume  basis  of  measurement. 


Measurement 


73 


107.  Volume  Basis.  Fluid  bituminous  materials  and 
sometimes  the  semisolids  and  solids  as  well  are  purchased 
upon  a  volume  basis  or  by  the  gallon.  In  the  last  analysis 
the  volume  of  bitumen  purchased  and  used  is  of  more  tech- 
nical importance  to  the  Engineer  than  is  its  weight.  The 
volume  basis,  however,  has  its  disadvantages,  and  the  actual 


12 


170 


190 


210, 


230 


250 


270 


0.9  1.0  1.1  1.2  1.3  1.4 

SPECIFIC  GRAVITY 

Fig.  7     Weight  and  Volume  Relations  for  Bituminous  Materials 

determination  of  volume  may  in  some  cases  necessitate  the 
use  of  weights.  When  this  is  done  the  specific  gravity  of 
the  material  must  of  course  be  taken  into  account.  The 
volume  content  of  certain  containers,  such  as  cylindrical 
tanks,  is  not  difficult  to  determine,  but  when  shipment  is 
made  in  small  containers  such  as  barrels,  frequently  of 
different  dimensions  and  filled  to  different  levels,  the  matter 
of  volume  measurement  in  bulk  becomes  so  difficult  as  to 


74 


Bituminous  Materials 


be  impracticable.  Moreover,  in  measuring  the  relatively 
small  quantities  used  in  mixing  batches  of  bituminous 
aggregate,  adhesion  of  the  material  to  the  inside  surface  of 
the  'container  is  such  a  variable  as  to  make  volume  measure- 
ment extremely  inaccurate.  In  addition,  before  measure- 
ment it  is  frequently  necessary  to  heat  the  material  to  a 


1.1  1.2  1.3 

SPECIFIC  GRAVITY  MATERIAL 


1.4 


Fig.  8     Weight  of  Bitumen  per  Gallon  of  Bituminous  Material 

relatively  high  temperature  to  render  it  sufficiently  fluid 
for  use.  .  Volume  changes  then  occur  which  depend  not 
only  upon  the  exact  increase  in  temperature,  but  upon  the 
response  to  such  increase  made  by  the  particular  material 
under  consideration.  This  change  in  volume  with  change 
in  temperature  is  a  function  of  the  coefficient  of  expansion 
which  varies  for  different  types  and  grades  of  bituminous 


Measurement 


75 


materials  (§  108).  Moreover,  if  purchase  is  made  upon  the 
basis  of  actual  bitumen  delivered  or  used,  the  volume 
method  of  measurement  becomes  involved  and  confusing. 
(6)  In  translating  weight  units  to  volume  units  and  vice 
versa,  the  specific  gravity  of  the  material  should  be  taken 
into  account.  These  relations  are  shown  in  Fig.  7. 


240 


1.15 


1.20 


1.25  1.30 

SPECIFIC  GRAVITY  A.C. 


1.35 


1.40 


Fig.  9     Volume  of  Bitumen  per  Ton  of  Asphalt 

If  impurities  are  present  to  a  known  extent  and  it  is  desired 
to  ascertain  the  weight  of  bitumen  per  gallon  of  material 
or  the  number  of  gallons  of  bitumen  per  ton  of  material, 
Figs.  8  to  10  will  be  found  useful.  The  diagrams  in  these 
figures  have  been  prepared  from  the  most  reliable  data 
obtainable  relative  to  the  specific  gravity  of  the  usual  im- 
purities present  in  the  types  of  materials  illustrated.  For 
all  practical  purposes,  petroleum  products  may  be  con- 


76 


Bituminous  Materials 


sidered  as  100  per  cent  bitumen  and  are,  therefore,  not 
shown  in  Figs.  8  to  10,  as  the  curves  would  be  identical  with 

Fig.  7. 

When  it  is  realized  that  the  actual  volume  of  bitumen 
present  in  a  road  surface  is  the  vital  consideration  so  far  as 
quantity  is  concerned,  the  importance  of  appreciating 
volume  and  weight  relations  becomes  apparent.  Thus, 


.10 


1.15 


1.20  1.25 

SPECIFIC  GRAVITY  TAR 


1.30 


1.35 


Fig.  10     Volume  of  Bitumen  per  Ton  of  Tar 

upon  reference  to  the  preceding  diagrams,  it  is  seen  that 
2000  pounds  of  an  oil  asphalt  of  1.03  specific  gravity  equal- 
ing 234  gallons  (Fig.  7)  is  the  equivalent  in  volume  of  bitu- 
men to  3020  pounds  of  Trinidad  asphalt  cement  of  1.3 
specific  gravity  and  70  per  cent  of  bitumen,  which  contains 
155  gallons  of  bitumen  per  ton  (Fig.  9).  This  means  that 
if  a  given  number  of  gallons  of  bitumen  per  square  yard  is 
required  to  construct  a  certain  type  of  pavement,  each  ton 
of  the  oil  asphalt  will  construct  1.5  more  yardage  than  a 
ton  of  the  Trinidad  product  or,  in  other  words,  for  each 


Measurement  77 

mile  of  a  given  pavement  constructed  with  the  latter,  1.5  miles 
can  be  constructed  with  the  same  tonnage  of  the  former. 

108.  Temperature  Corrections  of  Volume,  (a)  Whether 
liquid  or  not  at  ordinary  temperature,  all  bituminous  ma- 
terials containing  50  per  cent  or  more  of  bitumen  become 
fluid  upon  heating  to  a  sufficiently  high  temperature.  In 
many  instances  it  is  necessary  to  heat  them  in  order  that 
they  may  be  used  advantageously  in  highway  work.  When 
such  is  the  case,  they  may  have  to  be  measured  at  elevated 
temperatures.  Weight  measurements  are  not  affected  by 
temperature  considerations,  as  weight  is  a  constant.  Volume 
changes  take  place,  however,  with  changes  in  temperature 
and  if  a  bituminous  material  is  purchased  upon  a  volume 
basis  at  ordinary  temperature,  or  if  its  volume  rate  of  use 
is  to  be  determined  at  ordinary  temperature,  its  change  in 
volume  at  the  elevated  temperature  of  measurement  or  use 
must  be  taken  into  account.  This  will  depend  upon  the 
coefficient  of  cubical  expansion  of  the  particular  material 
(§  122).  This  coefficient  of  expansion  is  the  increase  in 
volume  which  a  unit  volume  undergoes  when  its  temperature 
is  raised  one  degree.  In  measuring  bituminous  materials 
by  volume,  60°  F.  (15.5°  C.)  is  usually  taken  as  the  standard 
or  normal  (§  120a)  temperature. 

(6)  In  the  vicinity  of  refineries,  certain  bituminous  ma- 
terials are  not  uncommonly  delivered  at  the  sight  of  the 
work  in  tank  wagons  or  tank  cars  at  a  temperature  ready  to 
apply.  In  such  cases  the  basis  of  purchase  should  be  clearly 
set  forth  in  the  specifications  and,  if  by  volume,  a  coefficient 
of  expansion  or  rate  of  increase  in  volume  with  temperature 
should  also  be  given.  In  most  cases  an  arbitrary  figure 
is  previously  agreed  upon.  Thus,  for  residual  petroleums 
the  coefficient  of  expansion  is  often  assumed  as  0.0004  per 
degree  F.  This  means  that  a  gallon  of  oil  at  60°  F.  will  ex- 
pand to  1.0004  gallons  at  61°  F.,  1.0008  gallons  at  62°  F., 
etc.  A  deduction  of  0.4  per  cent  is,  therefore,  made  for  every 
increase  of  10  degrees  over  60°  F.  in  ascertaining  the  volume 


78 


Bituminous  Materials 


at  normal  temperature.  As  an  example,  if  a  tank  wagon 
having  a  capacity  of  six  hundred  gallons  is  filled  with  the 
oil  at  a  temperature  of  260°  F.  the  volume  of  oil  at  60°  F. 
would  be  555.5  gallons.  For  such  determinations  use  may 


118 


116 


114 


112 


110 


O 

^  108 

o; 
ui 

CL 
CO 


104 


102 


100 


60 


150  250  350 

DEGREES  FAHRENHEIT 


450 


Fig.  11     Volumes  at  Elevated  Temperatures  Equivalent  to 
100  Gallons  at  Normal  Temperature 

be  made  of  the  following  formula  in  which  V  is  the  volume 
at  normal  temperature,  V',  the  observed  volume  at  an  ele- 
vated temperature  and  T  is  the  observed  temperature  in 
degrees  Fahrenheit. 


.0004(T  -  60)  +  1. 


Measurement 


79 


(c)  The  coefficients  of  expansion  of  materials  of  the  same 
type  and  grade  vary  somewhat,  but  in  practical  work  an 
average  coefficient  may  be  assumed  for  certain  classes  which 
is  sufficiently  close  for  ordinary  use.  Such  approximate 
coefficients  are  shown  in  the  Table  on  the  following  page. 


84  •  ' 

j 

OR  -  _. 

/ 

^ 

?        ^ 

Z    88  

O 

^"      ^ 

_, 

/        ^            ~f 

8QA     ...  _„_..  
90 

*•  i      t*          '     i.' 

^?^/          /      f 

O  V  *W      '  *j£  3  ^  ' 

UJ 

*  '  ^  9X   CrV  W*  ' 

0.                                                         T< 

"  >&  1  C/'^'' 

^92                                          t. 

Cu^  '  a<2    e 

/    ^JCafr'                       * 

/   / 

t    \ 

rf   94                                     // 

.  ?    ? 

7 

Z                                         L/    L^/ 

o                         lt    ?/ 

o             _L         1  1  i  i 

it   " 

/?/  / 

L  \ 

iK 

""  60               150                 2f 

>0                 350               460 

DEGREES  FAHRENHEIT 

Fig.  12     Volumes  at  Normal  Temperatures  Equivalent  to 
100  Gallons  at  Elevated  Temperatures 

Figures  11  and  12  illustrate  volume  and  temperature  rela- 
tions as  affected  by  the  various  coefficients  of  expansion 
given  in  the  Table.  The  first  shows  for  various  Fahrenheit 
temperatures  the  number  of  gallons  equal  to  100  gallons  at 
60°  F.  The  second  shows  the  number  of  gallons  at  60°  F. 
represented  by  each  100  gallons  at  increased  temperatures. 
When  temperatures  are  taken  by  Centigrade  thermometers, 


80 


Bituminous  Materials 


the  equivalent  of  the  Fahrenheit  scale  (§  1206)  should  be 
ascertained  before  using  these  diagrams  in  making  volume 
corrections. 

APPROXIMATE  COEFFICIENTS  OF  EXPANSION  OF  BITUMINOUS 
MATERIALS 


Material 

Coefficient  of  Expansion 

Per  °F. 

Per  °C. 

Creosoting  Oils           

0.00044 
.00039 
.00033 
.00030 
.00030 

0.00080 
.00070 
.00060 
.00055 
.00055 

Liquid  Residual  Petroleums  

Liouid  Refined  Tars 

Asphalt  Cements 

Heavy  Refined  Tars 

SAMPLING 

109.  Time  and  Place  of  Sampling.    Whenever  practica- 
ble, bituminous  materials  should  be  sampled  at  the  point  of 
manufacture,  and  at  such  time  as  to  allow  the  tests  con- 
trolling acceptance  or  rejection  to  be  made  in  advance  of 
shipment.     This  will  require  from  one  to  two  days  if  the 
laboratory  :is  near  at  hand.     When  impracticable  to  take 
samples  at  point   of  manufacture,   they  should  be  taken 
from  each  shipment  immediately  upon  delivery.  In  addi- 
tion, samples  should  be  taken  whenever  the  appearance  or 
general  character  of  the  material  changes  or  when  there  is 
reason  to  suppose  that  it  has  been  injured  by  overheating. 
Frequent  sampling  during  use  is  often  necessary  when  the 
Inspector  is  required  to  make  paving  plant  tests  having  to 
do  with  control  of  consistency.    Thus,  when  the  material  is 
fluxed  or  maintained  in  heating  kettles  at  an  elevated  tem- 
perature for  periods  of  twelve  hours  or  more,  at  least  one 
sample  should  be  taken  and  tested  for  consistency  each  day 
during  its  use. 

110.  Size   of  Samples.     Samples  of  approximately  one 
quart  or  two  pounds  in  weight  should  be  submitted  to  the 


Sampling  81 

Laboratory  except  when  only  a  check  test  of  consistency  is 
to  be  made  of  asphalt  cement  or  heavy  refined  tar.  In 
such  cases,  where  the  penetration,  melting  point,  or  float 
test  is  to  be  made,  three-ounce  samples  will  be  sufficient. 

Where  practice  other  than  the  above  is  to  be  followed  the 
Engineer  or  Laboratory  should  instruct  the  Inspector  as  to 
the  proper  size  of  laboratory  samples.  In  certain  cases,  two 
or  more  samples  from  a  given  shipment  may  be  submitted 
to  the  laboratory,  with  the  understanding  that  a  few  tests 
will  be  made  upon  each  to  determine  uniformity,  and  that 
the  complete  set  of  tests  will  only  be  made  upon  a  composite 
sample.  In  such  cases  the  size  of  the  individual  samples 
should  be  such  as  to  allow  for  the  tests  of  uniformity,  usually 
specific  gravity  and  consistency,  with  a  surplus  amply  suffi- 
cient to  prepare  a  single  composite  sample  of  the  same  size 
as  though  only  one  sample  were  submitted.  For  daily 
routine  laboratory  checks  of  plant  or  field  practice,  the 
most  desirable  size  of  sample  will  depend  upon  just  what 
check  tests  are  required. 

111.  Containers.     Containers  for  liquid  bituminous  ma- 
terials  should   be    1-quart,   small-mouth   cans   with    screw 
cap  or  cork  stopper.     For  semisolid  and  solid  materials, 
1-quart  friction  top  cans  will  be  found  useful.     Samples  of 
asphalt  cement  or  refined  tar  which  are  to  be  subjected  to 
check   penetration,   melting    point,  or    float    test  may   be 
placed    in     3-ounce    round    tin    boxes    with    tight-fitting 

cover. 

112.  General   Precautions.     In   general   samples   should 
be  taken  so  as  to  represent  as  nearly  as  possible  an  average 
of  the  bulk  of  material  sampled  and,  in  most  cases,  should 
also  be  selected  with  a  view  to  ascertaining  the  maximum 
variation  in  characteristics  which  the  material  may  possess. 
Great  care  should  be  taken  that  the  samples  are  not  con- 
taminated with  dirt  or  any  other  extraneous  matter  and 
that  the  sample   containers  are  perfectly   clean  and   dry 
before  filling.    When  kerosene  is  used  for  cleaning  sampling 


82  Bituminous  Materials 

tools,  it  should  be  completely  removed  by  wiping  before 
the  tools  are  again  used  for  sampling.  When  in  the  open, 
materials  should  be  sampled  preferably  during  dry  weather, 
but  if  taken  in  rainy  weather  care  should  be  exercised  to 
prevent  water  from  being  introduced  into  the  sample  can. 
Sampling  bituminous  materials  is,  at  best,  dirty  work  and 
extreme  care  should  be  taken  by  the  Inspector  that  his 
samples  do  not  become  contaminated  .with  water,  dirt, 
chips  of  wood,  paper,  or  other  extraneous  material  which 
would  tend  to  vitiate  test  results.  Immediately  after  fill- 
ing, the  sample  containers  should  be  tightly  closed  and 
properly  marked  for  identification.  They  should  be  packed 
for  shipment  in  such  manner  that  leakage  of  contents  or 
contamination  by  excelsior,  paper  or  other  packing  material 
during  transit  is  entirely  prevented,  as  well  as  obliteration 
or  removal  of  the  identification  marks. 

113.  Sampling   from   Pipe    Lines.     When   loading   tank 
cars,  barrels,  or  drums  from  a  storage  tank,  cooler,  or  still, 
or  when  unloading  tank  cars,  drip  samples  may  be  taken 
from  the  discharge  pipe.     The  material  should  be  allowed 
to  flow  for  a  short  time  before  the  first  sample  is  taken  in 
order  to  free  it  from  material  remaining  after  its  last  use. 
The  drip  valve  inserted  in  the  line  should  be  so  regulated 
that  the  operation  of  collecting  continues  through  the  entire 
period  of  discharge.     Unless  the  contents  of  a  tank,  cooler, 
or  still  are  thoroughly  agitated  during  the  period  of  discharge, 
at  least  three  drip  samples  should  be  taken,  each  represent- 
ing approximately  one  third  of  the  amount  discharged.     It 
is,  however,  advisable  that  no  single  sample  should  repre- 
sent more  than  one  tank  car  if  the  loading  of  tank  cars  is 
being  inspected. 

114.  Sampling  Directly  from  Tanks,     (a)  When  for  any 
reason  it  is  not  advisable  to  take  drip  samples  from  storage 
tanks  or  tank  cars,  samples  may  be  taken  directly  from  the 
tanks.     Unless  the  material  is  quite  liquid  and  being  thor- 
oughly agitated  during  sampling,  three  samples  should  be 


Sampling  83 

taken,  one  from  the  top,  one  from  the  bottom,  and  one  from 
the  center  of  the  tank.  For  materials  which  are  fluid,  the 
bottom  sample  may  be  taken  from  the  discharge  pipe, 
through  which  a  sufficient  amount  of  material  is  first  allowed 
to  flow  so  as  to  clean  it  properly.  Such  material  should  be 
discarded  or  returned  to  the  top  of  the  tank.  If  there  is  no 
outlet  at  the  middle  of  the  tank,  a  thief  sample  may  be 
taken  by  lowering  a  properly  weighted  closed  bottle  or  can 
to  the  center  of  the  tank  and  then  removing  the  stopper  or 
cover  by  means  of  a  stout  cord  or  wire  to  which  it  is  attached. 
The  necessity  of  sampling  from  different  levels  is  apparent 
when  it  is  considered  that  a  storage  tank  may  contain  the 
product  of  a  number  of  stills  and  even  a  tank  car  may  be 
partially  filled  from  the  last  portion  of  one  still  and  the 
difference  made  up  from  the  contents  of  another  still. 
Moreover,  incomplete  fluxing  may  have  been  conducted  in 
the  tank. 

(6)  If  samples  are  taken  from  tank  cars  or  distributors 
just  before  or  during  use  of  their  contents,  three  samples 
may  be  taken  from  the  discharge,  one  shortly  after  the 
material  begins  to  flow  from  the  discharge,  one  when  the 
contents  of  the  tank  are  about  half  removed,  and  one  when 
the  tank  is  nearly  empty.  In  the  case  of  distributors  of 
1000  gallon  capacity  or  less  the  three  samples  may  be  com- 
bined to  produce  a  single  composite  sample. 

(c)  Tanks  or  tank  cars  containing  cold  semisolid  or  solid 
bituminous  materials  should  be  heated  so  as  to  render  their 
contents  fluid  before  samples  are  taken.  If,  however,  for 
any  reason  it  is  desired  to  obtain  a  preliminary  sample  the 
material  may  be  sampled  through  the  dome  or  top  manhole 
by  the  use  of  a  perfectly  clean  hot  shovel. 

115.  Sampling  from  Barrels  and  Drums,  (a)  Separate 
samples  should  be  taken  from  not  less  than  3  per  cent  of  the 
containers  and,  when  sampling  from  car  loads,  one  sample 
should  be  taken  from  each  20  packages  and  fraction  of  20 
over  10  and  identified  with  the  car  number.  As  it  is  quite 


84  Bituminous  Materials 

possible  that  various  lots  of  different  grades  of  material  may 
have  become  inadvertently  mixed,  the  packages  to  be 
sampled  should  be  carefully  selected  with  reference  to  their 
position  in  the  shipment  and  the  manufacturer's  markings 
which  they  may  carry.  Such  markings  should  be  recorded 
for  every  container  sampled,  and  used  as  a  means  of  identi- 
fication. In  no  case  should  two  adjacent  containers  be 
sampled  unless  they  bear  different  markings,  or  appear  to 
contain  different  material. 

(6)  When  the  material  is  semisolid  or  solid,  samples 
should  be  taken  at  least  three  inches  below  the  surface. 
This  is  advisable  not  only  because  the  surface  may  be  con- 
taminated with  dirt,  but  because  when  a  container  is  first 
filled  with  hot  material  considerable  contraction  takes  place 
upon  cooling  and  the  container  may  afterwards  be  topped 
by  running  in  additional  material.  It  is  quite  possible  that 
through  mistake  the  material  used  for  topping  may  be  of 
a  different  grade,  and  samples  taken  from  the  top  will  not, 
therefore,  represent  the  consignment.  For  this  reason, 
when  shipment  is  made  in  double-head  barrels,  it  is  good 
practice  to  occasionally  up-end  a  barrel  selected  for  sampling, 
and  sample  from  what  was  the  bottom. 

(c)  Samples  of  solid  products  may  be  chipped  out  with  a 
hatchet.  If  the  material  is  too  soft  to  be  chipped  out  a 
central  portion  of  the  top  surface  from  5  to  10  inches  long 
and  2  to  4  inches  wide  may  be  removed  to  the  desired  depth 
by  means  of  a  hard,  stiff  putty  knife.  A  hatchet  or  small 
hand  axe  is  often  convenient  to  mark  out  the  portion  which 
is  to  be  removed.  The  first  cut  is  thrown  away  and  the 
sample  taken  from  the  bottom  of  the  hole  by  means  of  a 
putty  knife.  If  any  water  or  dirt  is  on  the  surface  of  the 
material  in  the  barrel  or  drum  selected  for  sampling,  it 
should  be  removed  so  that  the  surface  is  clean  and  dry.  A 
large  sponge  will  be  found  useful  for  this  purpose. 

116.  Sampling  from  Loose  Bulk.  When  a  hard  and  rela- 
tively pure  bituminous  material  such  as  Gilsonite  is  shipped 


Sampling 


85 


in  loose  fragments,  one  sample  should  be  taken  for  every 
five  or  six  tons  represented  by  the  shipment.  The  individual 
samples  should  be  taken  from  as  many  different  locations 
as  possible  in  the  car  or  pile.  Rock  asphalt  may  be  sampled 
in  like  manner,  except  that  one  sample  may  be  taken  for 
every  40  to  50  tons.  Owing  to  the  fact  that  rock  asphalts 
may  congeal  more  or  less  during  storage  and  shipment,  a 
pick  may  be  required  to  obtain  samples. 

117.  Prepared  Joint  Fillers.  At  least  three  samples 
should  be  taken  of  every  shipment  of  bituminous  expansion 
joints  or  prepared  joint  fillers.  Each  sample  should  consist 
of  a  strip  about  twelve  inches  in  length. 


CHAPTER  VI 

LABORATORY  TESTS  OF  BITUMINOUS 
MATERIALS 

SIGNIFICANCE  OF  LABORATORY  TESTS 

118.  Value  of  Tests.     Unlike  many  otheY  road  and  paving 
materials,  only  a  few  of  the  laboratory  tests  for  bituminous 
materials  directly  indicate  suitability  for  a  given  purpose, 
and    even  these    must    be    considered   with    special   refer- 
ence to  the  type  of  material  which  other  laboratory  tests 
serve  to  identify.     Among  the  tests  indicating  suitability, 
the  most  important  are  those  which  determine  consistency. 
For  certain  classes  of  work  such  tests  may  often  be  made 
by  the    Inspector    (§§  378-379).      In    like  manner,  certain 
tests  are  sometimes  made  which  serve  as  a  control  for  the 
use  of  the  material  but  do  not  necessarily  indicate  inherent 
suitability  (§  380) .     Tests  for  identification  purposes  which 
may  be  specified  are  usually  made  in  the  laboratory  only, 
but  the  Inspector  should  be  familiar  in  a  general  way  with 
the  methods  employed  in  making  such  tests  and  the  use  for 
which  the  test  results  may  serve. 

119.  Specification  Requirements.     Specification   require- 
ments for  bituminous  materials  have  not  been  as  generally 
standardized  as  for  other  highway  materials  and,  owing  to 
the  many  different  products  which  have  to  be  considered  as 
a  class,  embrace  a  large  number  of  tests.     Some  of  these 
tests  may  be  of  purely  local  significance,  as  they  are  used 
and  understood  only  by  the  Engineer  in  whose  laboratory 
the  test  was  devised.     In  general,  however,  the  Engineer, 

86 


Significance  of  Laboratory  Tests  87 

in  preparing  specifications,  selects  from  a  number  of  tests 
which  have  been  widely  used,  and  such  tests  are  briefly 
covered  in  the  following  paragraphs. 

120.  Temperature  Considerations,  (a)  It  has  been  noted 
(§  108)  that  changes  in  temperature  produce  marked  changes 
in  the  volume  of  bituminous  materials  and  that  for  the 
purpose  of  volume  measurements  60°  F.  (15.5°  C.)  is  taken 
as  normal  temperature.  Other  characteristics  of  bitumi- 
nous materials  are  also  affected  by  temperature,  particularly 
their  consistency.  For  laboratory  tests,  therefore,  it  has 
been  thought  advisable  to  adopt  a  normal  temperature  which 
is  commonly  understood  to  apply  unless  some  other  tem- 
perature is  specifically  mentioned.  As  applied  to  laboratory 
observations  of  the  physi'cal  characteristics  of  bituminous 
material,  the  American  Society  for  Testing  Materials  has 
adopted  25°  C.  (77°  F.)  for  normal  temperature,  Standard 
Definitions  D8-18.  This  .standard  is  almost  universally 
used. 

(b)  Most  specifications  state  temperature  requirements 
in  degrees  Fahrenheit,  particularly  when  they  apply  to 
field  control.  The  Inspector,  therefore,  ordinarily  uses  that 
scale  and  is  supplied  with  a  Fahrenheit  thermometer.  The 
Centigrade  scale  is,  however,  generally  employed  in  the 
laboratory,  and  specifications  for  bituminous  materials  as 
well  as  test  reports  frequently  state  temperature  in  degrees 
Centigrade.  In  any  event  it  may  be  necessary  for  the 
Inspector  to  translate  from  one  scale  to  the  other.  For  this 
purpose  the  following  formulas  should  be  used: 

°F  =  f  °C  +  32. 

5(°F-32) 
~9~ 

For  ordinary  purposes  the  equivalents  shown  in  Fig.  13  will 
be  found  sufficiently  accurate. 


Laboratory  Tests  of  Bituminous  Materials 


450 


400 


-250 


a  200 

a: 


150 


115°  F. 
100 


6O°F. 
50 


32  °F. 


50 


100  150 

DEGREES  CENTIGRADE 


200 


250 


Fig.  13    Equivalents  of  Fahrenheit  and  Centigrade  Scales 

DENSITY  TESTS 

121.  Specific  Gravity,  (a)  There  are  a  number  of  methods 
used  for  determining  the  specific  gravity  of  bituminous 
materials,  depending  largely  upon  their  consistency  at 
normal  temperature  (§  120a).  Thus,  for  thin  fluids  a  hy- 


Density  Tests  89 

drometer  may  be  employed  for  obtaining  direct  specific  grav- 
ity results.  The  more  viscous  fluids  and  semisolid  materials 
are  commonly  weighed  in  a  pycnometer  or  bottle  of  special 
design  and  known  capacity.  The  weight  of  material 
divided  by  the  weight  of  an  equal  volume  of  water  at  normal 
temperature  then  gives  the  specific  gravity  of  the  material. 
For  hard  solid  materials  a  fragment  may  be  weighed  in  air 
and  then  weighed  suspended  in  water  by  a  thread  or  fine 
wire.  When  this  is  done,  its  specific  gravity  is  obtained  by 
dividing  its  weight  in  air  by  the  difference  between  its  weight 
in  air  and  in  water.  In  order  that  there  may  be  no  misunder- 
standing as  to  the  basis  upon  which  the  determination  is 
made  test  results  are  frequently  reported  as  in  the  following 
example : 

Sp.  Gr.  25°  C./250  C 1.035 

This  means  that  the  determination  has  been  made  on  the 
basis  of  the  weight  of  a  definite  volume  of  the  material  at 
25°  C.  as  compared  with  the  weight  of  an  equal  volume  of 
water  also  at  25°  C.  In  some  few  cases  such  as  creosoting 
oils  specific  gravity  may  be  determined  and  reported  upon 
a  38°.C./38°C.  basis. 

(6)  For  liquid  materials  lighter  than  water,  particularly 
fluid  petroleum  products,  manufacturers  have  become 
accustomed  to  using  an  arbitrary  scale  of  specific  gravity 
known  as  the  Baume  scale.  For  this  purpose  they  make 
use  of  a  hydrometer  graduated  in  degrees  Baume.  Petro- 
leum products  for  highway  work  are,  therefore,  sometimes 
specified  and  sold  upon  a  degree  Baume  or  °B.  basis.  The 
Inspector  may  have  occasion  to  translate  direct  specific 
gravity  into  °B.  and  vice  versa,  in  which  case  the  following 
foimulas  apply: 

Q     r-  14Q 

=  130  +  °B 

oB  _  _ii°L  _  130 

Sp.  Gr. 


90    Laboratory  Tests  of  Bituminous  Materials 

For  ready  reference  the  diagram 'of  equivalents  shown  in 
Fig.  14  will  be  found  useful.  In  this  diagram  it  will  be  noted 
that  the  degrees  Baume  decrease  as  specific  gravity  increases. 


W         r 

r 

\ 

on                      1 

\ 

^ 

\_  . 

" 

\ 

MIJ                     "J"' 

r>                                ^ 

<      ^  .. 

LJ                                                           L 

Q;          ..        _L 

0                                                          > 

D                                                       -| 

y 

Af\    _.  ... 

s 

\ 

^ 

^ 

T   \ 

\ 

\ 

\~ 

\ 

OA     

"     ^ 

s 

^    . 

_  S--- 

10  

'  j 

.6                   .7                   .8                   .9                1.0 

SPECIFIC  GRAVITY 

Fig.  14     Specific  Gravity  Equivalents  of  Baume  Scale 
for  Liquids  Lighter  than  Water 


(c)  While  the  Inspector  is  seldom  required  to  make 
specific  gravity  determinations  of  bituminous  materials, 
he  may  frequently  make  use  of  laboratory  test  reports  to 
good  advantage  in  estimating  correct  proportions  and  in 


Consistency  Tests  91 

measuring  quantities  of  materials,  as  well  as  amount  of  work 
performed.  Such  uses  have  already  been  indicated  (§  107) 
and  will  further  appear  in  connection  with  paving  plant 
inspection  and  the  inspection  of  various  types  of  highways 
in  which  bituminous  materials  are  used.  In  addition,  the 
specific  gravity  test  is  a  valuable  means  of  identifying  the 
material,  particularly  in  connection  with  a  test  of  consist- 
ency. It  is  frequently  used  in  specifications  for  this  purpose 
as  well  as  for  the  sake  of  controlling  uniformity  of  supply 
from  a  given  source. 

122.  Coefficient  of  Expansion.  The  cubical  coefficient 
of  expansion  of  a  bituminous  material  is  seldom  specified 
except  for  the  purpose  of  making  volume  corrections  for 
elevated  temperatures  (§  108).  For  this  purpose  the  term 
"coefficient  of  expansion"  may  not  even  be  used,  but  instead 
the  volume  correction  which  will  be  made  for  certain  in- 
creases in  temperature  is  stated.  The  coefficient  of  expan- 
sion or  volume  increase  which  the  material  undergoes  for 
each  increase  of  one  degree  above  normal  temperature  may 
be  stated  in  terms  of  the  Fahrenheit  or  Centigrade  scale. 
To  translate  from  one  to  the  other  the  following  formulas 
apply  when  K  represents  the  coefficient  of  expansion. 


#per°F.  =fKper°C. 

The  coefficient  of  expansion  may  be  determined  by  heating 
a  known  volume  of  the  material  at  normal  temperature 
to  an  elevated  temperature  at  which  its  volume  is  then 
noted.  The  unit  increase  in  volume  divided  by  the  number 
of  degrees  above  normal  temperature  to  which  the  material 
was  heated  gives  its  coefficient  of  expansion. 

CONSISTENCY  TESTS 

123.  Viscosity.  The  viscosity,  ordinarily  expressed  as 
specific  viscosity,  of  liquid  bituminous  materials  is  deter- 
mined by  means  of  the  Engler  viscosimeter.  In  brief,  this 


92    Laboratory  Tests  of  Bituminous  Materials 

apparatus  consists  of  a  cylindrical  cup  with  a  small  outlet 
tube  of  standard  dimensions  fitted  to  the  bottom.  This 
outlet  tube  may  be  opened  or  closed  with  a  pointed  hard- 
wood stopper.  The  cup  is  jacketed  with  a  water  bath  for 
controlling  the  temperature  at  which  the  test  is  to  be  made 
and  the  entire  apparatus  is  suitably  mounted  on  a  tripod 
so  that  a  measuring  cylinder  may  be  placed  under  the  outlet. 
The  test  consists  in  placing  a  given  volume  of  bituminous 
material  in  the  cup  and  bringing  it  to  the  proper  tem- 
perature for  test.  The  outlet  tube  is  then  opened  and 
the  time  required  for  a  given  volume  of  oil  to  flow  into  the 
measuring  cylinder  is  ascertained  with  a  stop  watch.  The 
number  of  seconds  is  then  a  measure  of  the  viscosity,  or 
resistance  to  flow,  of  the  material  and  test  results  are  some- 
times expressed  in  seconds.  It  is  more  customary,  however, 
to  divide  this  time  by  the  time  required  for  the  same  volume 
of  water  at  normal  temperature  to  flow  through  the  outlet, 
the  quotient  obtained  being  specific  viscosity.  Specifica- 
tions and  test  reports  should  always  indicate  whether 
results  are  expressed  in  seconds  or  in  terms  of  specific  vis- 
cosity as  well  as  the  measured  quantity  of  material  passing 
the  outlet  and  its  temperature.  Thus,  if  the  test  is  made 
upon  a  material  at  40°  C.  and  220  seconds  is  required  for 
50  cubic  centimeters  to  pass  the  outlet  tube,  the  test  result 

should  be  expressed  as  follows: 

p  to  dteobift'jo-i  oHl 

Viscosity  Engler  40°  C.,  50  c.c 220" 

If  it  is  found  that  11  seconds  are  required  for  the  passage 
of  50  cubic  centimeters  of  water,  then  results  may  be  ex- 
pressed as  specific  viscosity  by  dividing  220  by  11,  thus: 

Specific  Viscosity  Engler,  40°  C.,  50  c.c 20 

It  is  evident  that  as  the  consistency  of  a  material  increases 
from  very  liquid  toward  semisolid,  its  viscosity  or  specific 
viscosity  also  increases.  The  viscosity  test  is  widely  used 
for  specifying  and  controlling  the  consistency  of  dust  pre- 


Consistency  Tests  93 

jventives  and  carpeting  mediums.     The  test  itself  is  ordi- 
|  narily  made  in  the  laboratory  and  seldom  by  the  Inspector. 
'  The  temperatures  of  test  most  commonly  used  are  25°  C 
40°  C.,  and  100°  C. 

124.  Float  Test.     The  float  test  is  used  for  determining 
the  consistency  of  those  products  which  are  too  viscous  for 
satisfactory  use  in  the  Engler  viscosimeter  and  not  suffi- 
ciently solid  for  the  penetration  test.     Such  products  are 
mainly  heavy  refined  tars  used  as  cements  or  seal  coating 
materials.     The  test  is  most  frequently  performed  in  the 
laboratory,  but  maybe  used  in  the  field  for  important  work 
such  as  bituminous  concrete.    It  is,  therefore,  described  in 
detail   under   Field   Tests    (§379).     This   test   consists   in 
determining  the  time  required  for  a  small  plug  of  the  ma- 
terial held  in  a  standard  mold  which  is  floated  upon  water 
to  soften  sufficiently  at  a  given  temperature  to  allow  water 
to  enter  the  float  and  cause  it  to  sink.    The  test  tempera- 
tures most  commonly  specified  are  32°  C.,  50°  C.,  and  100°  C. 

125.  Penetration  Test.     This  test  has  been  adopted  by 
the  American  Society  for  Testing  Materials  as  Standard 
Test  D5-16  and  is  widely  used  for  determining  the  con- 
sistency of  asphalts  and  asphalt  cements.     It  is  not  only 
made  in  the  Laboratory,  but  at  paving  plants  as  well  and 
it  is,  therefore,  fully  described  under  Field  Tests  (§  378). 
In  the   standard  test,  penetration  is  defined  as  "the  con- 
sistency of  a  bituminous  material,  expressed  as  the  distance 
that  a  standard   needle  vertically  penetrates  a  sample  of 
the  material  under  known  conditions  of  loading,  time,  and 
temperature.    When  the  conditions  of  test  are  not  specifi- 
cally mentioned,  the  load,  time,  and  temperature  are  under- 
stood to  be  100  grams,  5  seconds,  25°  C.  (77°  F.),  respectively, 
and  the  units  of  penetration  to  indicate  hundredths  of  a 
centimeter."    Thus  an  asphalt  cement  of  50  penetration  is 
one  which  at  25°  C.  will  allow  a  standard  needle  operating 
under  a  weight  of  100  grams  to  penetrate  it  for  a  distance 
of  50  hundredths  of  a  centimeter  in  5  seconds. 


94    Laboratory  Tests  of  Bituminous  Materials 

126.  Melting  or  Softening  Point,  (a)  Three  methods 
for  determining  the  melting  or  softening  point  of  bituminous 
materials  are  in  common  use,  the  cube-in-air  method,  the 
cube-in-water  method,  and  the  ring-and-ball  method.  Re- 
sults upon  the  same  material  by  the  three  methods  often 
differ  widely  because  there  is  no  definite  temperature  at 
which  an  apparently  solid  bituminous  material  suddenly 
becomes  fluid.  These  materials  soften  gradually  with  in- 
crease in  temperature,  so  that  various  conditions  attending 
the  method  of  making  a  test  will  influence  the  final  result. 
For  this  reason  the  exact  method  should  always  be  indi- 
cated in  specifications  and  test  reports. 

(6)  In  the  cube-in-air  method,  a  J-inch  cube  of  the  ma- 
terial is  suspended  in  air  upon  a  wire  1  inch  above  the 
bottom  of  a  glass  beaker  or  jar,  which  in  turn  is  placed  in 
another  beaker  of  water.  A  thermometer  is  also  suspended 
beside  the  cube  of  material.  The  water  in  the  outer  vessel 
is  then  heated  so  that  the  air  temperature  in  the  inner 
vessel  increases  at  the  rate  of  5°  C.  (9°  F.)  per  minute,  and 
when  the  cube  softens  sufficiently  so  that  it  touches  the 
bottom  of  the  beaker  the  temperature  is  recorded  as  its 
melting  or  softening  point.  The  cube-in-water  method  is 
the  same  as  the  cube-in-air  method,  except  that  the  outer 
beaker  is  dispensed  with  and  the  beaker  containing  the 
specimen  is  filled  with  water.  The  ring-and-ball  method  is 
also  quite  similar,  except  that  the  material  is  cast  in  a  stand- 
ard ring  mold  and  both  the  mold  and  contents  are  suspended 
in  the  beaker  beside  the  thermometer.  A  standard  steel 
ball  or  shot,  of  smaller  diameter  than  the  ring,  is  placed  upon 
the  surface  of  the  material  before  heat  is  applied.  The  rate 
of  increase  of  temperature  is  the  same  as  in  the  cube  method, 
and  the  melting  point  of  the  material  is  ascertained  in  the 
same  general  manner.  With  the  ring-and-ball  method,  the 
outer  jacket  is  dispensed  with  and  the  beaker  containing 
the  specimen  itself  is  filled  with  water. 

(c)  The  melting  or  softening  point  of  bituminous  fillers 


Heat  Tests  95 

and  tar  pitches  is  commonly  specified  and  the  test  is  used  to 
some  extent  on  asphalts  and  asphalt  cements  for  paving 
work,  where  it  serves  to  control  uniformity  of  supply 
and  method  of  manufacture.  Blown  asphalts  usually  show 
a  much  higher  melting  point  than  residual  asphalts  of  the 
same  penetration.  The  melting  point  may  be  specified  and 
reported  either  in  °C.  or  °F. 

127.  Ductility.     A  ductility  requirement  is  often   speci- 
fied  for    asphalt    cements.     When    such    is    the   case,   the 
test  is  made  by  pulling  apart  a  briquette  of  the  material 
having  a  minimum   cross   section   of   1    square   centimeter 
and  ascertaining  the  distance  in  centimeters  which  it  will 
stretch  without  breaking.     Thus  a  ductility  of  50  indicates 
that  the  material  will  stretch  50  centimeters  before  failure 
occurs.    The  test  is  commonly  made  with  the  material  under 
water  at  25°  C.,  the  rate  of  pull  being  5  centimeters  per 
minute.    Various  machines  have  been  devised  for  this  test, 
all,  however,  based  on  the  same  general  principle  of  produc- 
ing a  steady  uniform  pull.     When  subjected  to  the  test, 
most  fluxed  native  asphalts  and  asphalt  cements  produced 
by  careful  distillation  of  asphaltic  petroleums  pull  out  to  a 
long  thin  thread  before  breaking,  while  highly  blown  as- 
phalts, which  are  characteristically  short,  rupture  without 
pulling  to  a  thread.    For  a  given  type  of  material  ductility 
decreases  with  hardness  or  decrease  in  penetration. 

HEAT  TESTS 

128.  Flash  and  Burning  Points.     As  determined  by  test 
the  flash  point  of  a  bituminous  material  is  the  temperature 
to  which  it  must  be  heated  in  order  that  the  vapors  liber- 
ated at  its  surface  will  flash  or  ignite  when  a  small  flame  is 
brought  in  contact  with  them.     The  burning  point  is  that 
temperature  to  which  the  material  must  be  heated  in  order 
to  catch  fire  and  burn  when  a  small  flame  is  brought  in 
contact  with   its  surface.     For  all   but  extremely  volatile 
products  there  is  usually  a  considerable  difference  between 


96    Laboratory  Tests  of  Bituminous  Materials 

the  flash  point  and  burning  point  temperatures.  The  test 
is  made  in  two  types  of  apparatus  known  as  the  open  cup 
and  the  closed  tester.  As  the  type  of  apparatus  largely 
affects  the  test  results,  it  should  be  indicated  in  specifica- 
tions and  test  reports.  Results  obtained  with  the  open 
cup  are  usually  higher  than  with  the  closed  cup.  Flash 
point  and  burning  point  requirements  are  used  as  a  means 
of  insuring  or  eliminating  the  presence  of  volatile  constitu- 
ents in  the  product,  as  may  be  desired.  Thus  a  cut-back 
asphalt  for  cold  surface  application  may  be  required  to 
show  a  low  flash  point,  while  a  high  flash  point  may  be  re- 
quired of  an  asphalt  cement  for  bituminous  concrete.  Flash 
points  and  burning  points  may  be  specified  and  reported 
either  in  °  C.  or  °F. 

129.  Volatilization  Test,  (a)  The  volatilization  test, 
which  is  commonly  applied  to  petroleum  and  asphalt  prod- 
ucts, determines  the  loss  by  volatilization  which  occurs 
when  a  given  weight  of  the  material,  placed  in  a  container 
of  given  dimensions,  is  maintained  at  a  specified  tempera- 
ture for  a  stated  length  of  time.  Such  a  test  has  been 
adopted  by  the  American  Society  for  Testing  Materials,  as 
Standard  Test  D6-16.  In  this  standard  a  50-gram  sample 
is  tested  at  a  temperature  of  163°  C.  (325°  F.)  for  five 
hours  and  the  loss  by  volatilization  is  expressed  as  per  cent 
of  the  original  material.  Sometimes  other  temperatures  and 
lengths  of  tests  are  specified,  and  test  reports  should  always 
indicate  just  how  the  results  have  been  obtained.  Thus 

Loss  at  163°  C.,  5  hours .  .  . .  2.7% 

THfimj  srf  r  *i ••iiifi'itom  *n  '  '      ui? 

(6)  After  a  volatilization  test  has  been  made  the  residue 
remaining  is  often  subjected  to  one  of  the  tests  for  con- 
sistency and  the  results  obtained  compared  with  the  con- 
sistency of  the  original  material.  The  volatilization  test 
then  not  only  indicates  how  much  of  a  material  is  likely  to 
evaporate  or  volatilize  at  an  elevated  temperature,  but  how 
much  it  may  harden  through  such  loss  by  volatilization. 


Heat  Tests  97 

Thus,  a  cut-back  asphalt  may  be  required  to  show  a  rela- 
tively high  loss  by  volatilization  with  a  change  from  liquid 
to  semisolid  consistency,  while  an  asphalt  cement  or  an 
ordinary  flux  will  be  required  to  show  low  loss  by  volatiliza- 
tion and  relatively  little  hardening  due  to  such  loss. 

130*  Asphalt  Contents.  Closely  related  to  the  volatili- 
zation test  is  the  determination  of  the  so-called  per  cent  of 
asphalt.  This  test  is  sometimes  made  upon  liquid  petroleum 
residues  as  a  measure  of  consistency  at  normal  temperature, 
but  it  is  not  a  very  reliable  indication  except  for  certain  types 
of  oil.  In  general,  it  is  made  by  heating  in  an  open  dish  a 
weighed  quantity  of  the  material,  at  a  temperature  not  ex- 
ceeding 260°  C.  (500°  F.).  At  intervals  the  sample  is  allowed 
to  cool  and  its  penetration  taken  at  25°  C.  When  the  residue 
shows  a  penetration  of  approximately  100  it  is  weighed. 
This  weight  is  then  calculated  to  per  cent  of  the  original 
sample  and  reported  as  the  per  cent  of  asphalt,  thus: 

Per  cent  of  asphalt  of  100  penetration 80% 

The  test  is  apt  to  be  misleading,  as  a  fluid,  nonvolatile  oil 
may  show  a  high  asphalt  content  but  develop  little  or  no 
binding  value  in  service,  while  a  more  volatile  fluid  product 
may  show  a  much  lower  asphalt  content  but  actually  pro- 
duce such  asphalt  under  service  conditions  so  as  to  develop 
considerable  binding  value. 

131.  Determination  of  Water.     The   presence   of  water 
in  a  bituminous  material  may  usually  be  detected  by  the 
foaming  which  takes  place  when  it  is  heated  to  approxi- 
mately 100°  C.  (212°  F.).     The  percentage  of  water  is  de- 
termined by  carefully  distilling  a  measured  quantity  of  the 
material  in  a  special  dehydrating  apparatus  and  measuring 
the  water  which  is  caught  as  distillate. 

132.  Distillation,     (a)  The    distillation    test    is    usually 
specified   for  refined  tars  and  has  been   adopted  by  the 
American  Society  for  Testing  Materials  as  Standard  Method 
D20-18.    It  consists  in  placing  a  known  volume  and  weight 


98    Laboratory  Tests  of  Bituminous  Materials 

of  the  material  in  a  standard  distilling  flask,  heating  the 
contents  gradually  and  collecting,  measuring  and  weighing 
the  distillates  coming  over  between  certain  temperatures. 
The  percentage  of  such  distillates  may  be  specified  and 
reported  either  upon  a  volume  or  weight  basis.  The  tem- 
peratures which  are  selected  as  well  as  the  method  of  report- 
ing test  results  are  shown  in  the  following  example: 


DistiUate 

Per  Cent 

By  Volume 

By  Weight 

Up  to  110°  C. 
From  110°  C. 
From  170°  C. 
From  270°  C. 
Pitch  residue 

0.7 
1.2 

23.8 
15.9 

58.4 

0.5 
0.8 
19.9 
14.8 
64.0 

to  170°  C                     

to  270°  C  

to  300°  C  

100.0 

100.0 

Specifications  for  cut-back  asphalts  sometimes  require  cuts 
to  be  made  at  other  temperatures.  For  distilling  creosote 
oils  the  American  Society  for  Testing  Materials  Standard 
Method  D38-18  is  commonly  used.  This  method  is  quite 
similar  to  that  already  described  except  that  a  standard 
retort  is  used  in  place  of  the  distilling  flask  and  distillates 
are  collected  at  210°,  235°,  270°,  315°  and  355°  C. 

(6)  As  a  part  of  the  distillation  test  the  specific  gravity 
of  certain  distillates  and  the  consistency  of  the  pitch  resi- 
due may  be  specified  and  determined.  As  applied  to  tars 
the  distillation  test  is  valuable  both  as  a  means  of  controll- 
ing their  method  of  manufacture  and  suitability  for  a  given 
purpose.  In  this  connection  it  takes  the  place  of  the  volatili- 
zation test  (§  129),  which  is  usually  restricted  to  petroleum 
and  asphalt  products. 

SOLUBILITY  TESTS 

• 

133.  Total  Bitumen.  The  per  cent  of  bitumen  in  a  bitumi- 
nous material  is  determined  in  the  laboratory  by  treating  a 


Solubility  Tests  99 

weighed  sample  of  the  material  with  carbon  disulphide,  which 
dissolves  all  the  bitumen  present.  The  dissolved  bitumen 
is  then  separated  from  any  insoluble  matter  by  filtration  in 
a  suitable  apparatus.  Any  residue  is  then  washed  clean 
with  carbon  disulphide  and  after  drying  is  weighed.  Its 
weight  subtracted  from  that  of  the  original  sample  gives 
the  weight  of  total  bitumen,  which  is  reported  upon  a  per- 
centage basis.  The  residue  may  next  be  ignited  to  burn  off 
organic  matter  and,  after  cooling,  again  weighed  and  re- 
ported as  per  cent  of  insoluble  inorganic  matter.  The 
amount  burned  off  is  determined  by  difference  and  reported 
as  per  cent  insoluble  organic  matter  or,  in  the  case  of  tars, 
as  free  carbon. 

(6)  In  the  case  of  bituminous  aggregates  the  insoluble 
residue  after  weighing  may  be  subjected  to  a  mechanical 
analysis  to  determine  its  grading.  Frequently  a  special 
form  of  extraction  apparatus  is  used  for  filtering  or  remov- 
ing the  dissolved  bitumen  from  the  nonbituminous  aggre- 
gate. 

(c)  While  the  Inspector  is  not  ordinarily  required  to 
make  determinations  of  total  bitumen,  he  may  frequently 
have  to  make  use  of  laboratory  reports  of  same.  Thus,  if 
purchase  of  the  material  is  made  upon  its  per  cent  of  total 
bitumen,  the  determination  may  be  necessary  as  a  basis 
of  measurement  and  payment  (§  106 c).  It  is  always  neces- 
sary as  a  basis  of  controlling  the  proportion  of  bituminous 
material  which  should  be  used  in  bituminous  concrete  or 
sheet  asphalt  and  is  used  by  the  laboratory  as  a  check  upon 
paving  plant  operations.  In  connection  vith  specific  gravity 
determinations  of  the  constituents  of  a  bituminous  aggre- 
gate, it  is  also  valuable  as  a  means  of  determining  the  per 
cent' of  voids  in  sections  of  finished  pavements  (§384). 

134.  Asphaltenes  or  Bitumen  Insoluble  in  Paraffin  Naph- 
tha. This  determination  is  made  only  upon  petroleum  and 
asphalt  products  and  in  specifications  is  usually  limited  to 
residual  petroleums.  In  general  the  method  is  the  same 


100    Laboratory  Tests  of  Bituminous  Materials 

as  for  the  determination  of  total  bitumen  (§  133  a)  except 
that  petroleum  naphtha  is  used  as  a  solvent  instead  of  car- 
bon disulphide.  The  bitumen  of  asphaltic  products  is  only 
partially  soluble  in  petroleum  naphtha  and  that  portion 
which  is  insoluble  is  commonly  known  as  asphaltenes.  -The 
solubility  of  any  asphaltic  product  in  naphtha  varies  with 
the  character  and  specific  gravity  of  the  naphtha  itself  so 
that  certain  grades  have  been  selected  for  the  test.  The 
one  most  commonly  used  is  known  as  86°  B.  or  88°  B. 
(§  121 6)  naphtha,  although  72°  B.  naphtha  is  sometimes  used. 
Test  results  are  reported  as  per  cent  of  bitumen  insoluble 
and  not  as  per  cent  of  the  original  material  which  is  insolu- 
ble in  the  naphtha.  In  general  the  higher  the  percentage 
of  asphaltenes  present  in  a  petroleum  product  the  more 
asphaltic  is  its  character  and  specifications  sometimes  make 
use  of  the  test  in  order  to  secure  a  highly  asphaltic  product. 

135.  Carbenes  or  Bitumen  Insoluble  in  Carbon  Tetra- 
chloride.     This  test  is  made  upon  petroleum  and  asphalt 
products  and  is  reported  upon  the  basis  of  per  cent  of  bitu- 
men insoluble,  in  exactly  the  same  manner  as  described  for 
asphaltenes  (§  134).     Most  petroleum  and  asphalt  products 
are  equally  soluble  in  carbon  disulphide  and  carbon  tetra- 
chloride,  but  if  badly  cracked  or  injured  by  overheating  dur- 
ing manufacture   they   become  less   soluble  in   the  latter 
solvent.     The  presence  of  such  insoluble  bitumen,   called 
carbenes,  is  sometimes  limited  in  specifications. 

136.  Dimethyl  Sulphate  Test.     This  test  is  made  upon 
bituminous  materials  which  may  be  specified  or  thought  to 
be  mixtures  of  tar  with   petroleum   or  asphalt   products. 
It  consists  first  in  distilling  the  material  (§  132  a)  and  col- 
lecting distillate  fractions  from  270°  to  300°  C.,  from  300° 
to  350°  C.  and  from  350°  to  375°  C.     These  distillates  are 
then  treated  with  dimethyl  sulphate.     Tar  distillates  are 
completely  soluble   in   this   reagent,  while   petroleum   and 
asphalt  distillates  are  insoluble.    Mixtures  of  the  two  classes 
will,  therefore,  yield  distillates  which  are  only  partly  soluble 


Miscellaneous  Tests  101 

and  when  treated  with  dimethyl-  sulphate  the  insoluble  por- 
tion separates  in  a  distinct  layer. 


MISCELLANEOUS  TESTS 

137.  Fixed  Carbon.     This  is  an  arbitrary  test  sometimes 
specified  in  connection  with  petroleum  and  asphalt  products. 
It  is  made  by  heating  a  weighed  sample  of  the  material  in  a 
covered  platinum  crucible  until  all  volatile  matter  is  burned 
off  and  only  residual  coke  is  left.    This  coke  is  weighed  and 
after  subtracting  any  ash  which  may  be  left  after  ignition 
in  the  uncovered  crucible,  the  results  are  reported  as  per- 
centage of  fixed  carbon  upon  the  basis  of  bitumen  present. 
The  test  is  not  exceedingly  accurate  and  is  used  mainly  as 
a  means  of  determining  the  asphaltic  character  of  the  prod- 
uct.    Thus,    products   manufactured    from   paraffin    petro- 
leums show  little  or  no  fixed  carbon,  while  solid  asphalts  may 
show  15  per  cent  or  more.    As  a  rule  semiasphaltic  products 
produce  less  fixed  carbon  than  asphaltic  products  of  the 
same  consistency. 

138.  Paraffin  Scale.     At  one  time  specifications  for  petro- 
leum and  asphalt  products  commonly  limited  the  per  cent 
of  paraffin  scale  which  might  be  allowed.     Owing  to  the 
inaccuracy  of  the  test  and  to  the  fact  that  such  a  limitation 
is  not  now  considered  so  necessary,  if  the  material  meets 
other  requirements,   its  use  has  been  largely  abandoned. 
When  specified,  the  test  is  made  by  rapidly  distilling  a 
weighed  sample  of  the  material  to  coke  and  collecting  the 
entire  distillate.    A  weighed  sample  oi  the  distillate  is  then 
chilled  to  20°  C.   and  treated  with  a  mixture  of  absolute 
alcohol  and  ether  at  the  same  temperature.     Any  paraffin 
scale  which  is  present  then  precipitates  out  and  is  quickly 
filtered  off.     Its  weight  is  calculated  as  per  cent  of  the 
original  sample. 

139.  Special   Tests   for   Emulsions.    Various  tests  of  a 
chemical  nature  which  are  of  little  direct  interest  to  the 


102     Laboratory  Tests  of  Bituminous  Materials 

Inspector  are  sometime^  specified  in  connection  with  emul- 
sions. The  more  important  tests  are  the  determination  of 
water,  determination  of  total  Bitumen,  distillation,  and  a 
test  for  consistency  of  the  residue  obtained  by  distillation 
to  a  given  temperature.  It  is  also  sometimes  required  that 
when  the  emulsified  product  is  mixed  with  a  certain  pro- 
portion of  water  no  separation  shall  occur  during  a  certain 
period  of  standing  and  that  when  mixed  with  a  clean  mineral 
aggregate  the  bitumen  shall  adhere  firmly  to  the  surfaces  of 
the  mineral  particles. 

140.  Special  Tests  for  Creosoting  Oils.  Certain  special 
tests  for  creosoting  oils  which  have  not  been  covered  in  the 
preceding  paragraphs  are  sometimes  specified.  These  are 
of  little  interest  to  the  Inspector  unless  he  is  required  to 
make  them  at  the  creosoting  plant  (§  322).  The  most  im- 
portant of  these  is  the  determination  of  solubility  of  the 
material  in  benzol  or  chloroform.  In  general,  this  test  is 
similar  to  the  determination  of  total  bitumen  (§  133)  except 
that  benzol  or  chloroform  is  used  as  a  solvent  instead  of 
carbon  disulphide.  Filtration  or  separation  of  the  insolu- 
ble material  is  made  in  a  special  type  of  apparatus  known 
as  a  hot  extractor.  Such  a  method  has  been  adopted  by 
the  American  Society  for  Testing  Materials  as  Standard 
Method  D38-18.  Other  tests  which  may  be  mentioned 
are  the  determination  of  tar  acids,  the  determination  of 
naphthalene  and  the  sulphoration  test. 

,!>•:> ft  in':*qh  nofiW 
fiira  l>tute// 


CHAPTER  VII 

INSPECTION  OF  SAND-CLAY,  GRAVEL, 
SHELL  AND  SHOVEL-RUN  OR  CRUSHER- 
RUN  SLAG  ROADS 

SAND-CLAY  AND  TOPSOIL  ROADS 

141.  General  Characteristics.  Sand-clay  and  topsoil 
roads  are  earth  roads  composed  essentially  of  sand  (§  46) 
and  clay  (§  49)  in  such  proportions  as  to  produce  much 
greater  stability  under  varied  seasonal  and  climatic  con- 
ditions than  is  afforded  by  ordinary  earth  or  soil.  In  sand- 
clay  roads  the  mixture  of  sand  and  clay  may  be  either 
natural  or  artificial.  Such  mixtures  occurring  at  the  sur- 
face of  cultivated  fields  are  called  topsoils.  Theoretically, 
the  best  mixture  consists  of  a  sand  body  containing  just 
sufficient  plastic  clay  to  fill  the  voids  and  bind  the  sand  and 
silt  grains  together.  After  compaction  such  a  mixture, 
when  wet,  possesses  the  stability  of  sand  and,  when  dry,  the 
stability  of  clay.  Under  traffic,  during  rainy  weather  it  does 
not  become  as  soft  and  muddy  as  a  clay  road  nor  as  dusty 
in  dry  weather.  The  presence  of  gravel  (§  42)  in  the  mix- 
ture is  rather  desirable  than  otherwise,  as  it  increases  stabil- 
ity or  resistance  to  displacement  urder  traffic.  Mixtures 
containing  a  considerable  amount  of  gravel  are  sometimes 
termed  semi-gravel.  The  relative  proportions  of  sand  and 
clay  should,  however,  remain  the  same  as  though  no  gravel 
were  present.  These  proportions  are  approximately  two 
parts  of  sand  to  one  of  ordinary  clayey  soil.  The  proportion 
of  true  clay  (§  42),  however,  is  considerably  less  than  one 
part  to  two  of  sand  (§  143). 

103 


104         Sand-clay,  Gravel,  Shell,  or  Slag 

142.  Construction    Methods.    There    are    three    general 
methods  of  constructing  sand-clay  roads,  depending  upon 
the  character  of  the  original  soil  and  that  of  available  local 
material.    If  the  original  soil  happens  to  be  a  natural  sand- 
clay  mixture,  the  construction  methods  are  the  same  as  for 
any  other  earth  road.    If  not,  the  following  conditions  may 
be  encountered. 

A  deposit  of  natural  sand-clay  or  suitable  topsoil  may 
be  available  for  use  on  the  original  soil. 

If  the  original  soil  is  not  suitable  for  admixture  with  sand 
or  clay,  both  products  may  have  to  be  placed  and  mixed  on 
the  road. 

The  original  soil  may  be  such  that  if  mixed  with  sand  or 
clay  a  suitable  combination  may  be  secured. 

In  the  first  case  the  graded  roadbed  may  be  trenched  out 
to  suitable  width  and  depth  and  filled  with  the  natural  sand- 
clay  or  topsoil,  or  it  may  merely  be  covered  with  the  desired 
thickness  of  such  material.  In  the  second  case,  one  or  more 
layers  of  sand  and  clay  are  spread  separately  in  the  trenched 
roadbed  and  thoroughly  mixed  by  means  of  plow  and 
harrow.  In  the  third  case  a  course  of  either  sand  or  clay, 
as  may  be  needed,  is  spread  upon  the  graded  roadbed  and 
mixed  with  the  original  soil  by  plowing  into  it  for  a  suitable 
depth  (§  145)  and  then  harrowing  all  of  the  loose  material. 
In  all  cases  traffic  is  usually  depended  upon  to  puddle  and 
compact  the  surfacing  material,  and  until  this  is  accom- 
plished the  road  should  be  frequently  dragged  or  shaped 
with  a  grading  machine.  A  second  plowing  and  harrowing 
after  the  first  soaking  rain  is  advisable,  and  possibly  the 
spreading  and  mixing  of  additional  clay  or  sand,  as  may  be 
indicated  by  the  behavior  of  the  mixture  under  traffic. 

143.  Selection  of  Materials.     The  selection  of  materials 
will  ordinarily  depend  first  of  all  upon  the  character  of  the 
original  soil.    While  some  soils  are  suitable  for  use  in  a  sand- 
clay  mixture,  others  are  wholly  unsuitable.     Thus,  a  clean 
hard  sand  or  a  plastic  clay  may  be  used  to  advantage  if  the 


Sand-Clay  and  Topsoil  Roads  105 

other  constituent  of  the  mix  is  locally  available.  A  clayey 
sand  or  a  sandy  clay  may  also  frequently  be  used  by  increas- 
ing the  proportion  of  one  or  the  other  constituent.  Soils 
containing  a  high  percentage  of  silt,  nonplastic  clay  or 
loam  are  unsuitable.  In  such  cases  natural  sand-clay,  top- 
soil,  or  sand  and  clay  separately  should  be  used.  An  excess 
of  very  fine  sand,  silt,  or  loam  will  produce  a  mushy  road  in 
wet  weather,  while  an  excess  of  lean  or  nonplastic  clay  will 
produce  a  dusty  road  in  dry  weather.  With  available  local 
material  it  is  not  always  possible  to  approximate  an  ideal 
mixture  and  at  best  no  absolutely  uniform  proportion  of 
sand  and  clay  is  likely  to  be  secured.  Certain  ranges  of 
proportions  must,  therefore,  be  allowed  in  practical  work. 
The  first  conference  of  State  Highway  Testing  Engineers 
and  Chemists  recommended  the  following  ranges  for  the 
material  passing  a  10-mesh  sieve  in  three  classes  of  mixtures. 
In  these  allowances  total  sand  includes  silt. 


Material 

Hard  or 
Class  A 

Medium  or 
Class  B 

Soft  or 
Class  C 

Per  cent 

Per  cent 

Per  cent 

Clay 

&-15 

15-25 

10-25 

Silt                          

5-15 

10-20 

10-20 

Total  Sand  
Sand  retained  on  60-mesh  sieve  .  .  . 

65-80 
45-60 

60-70 
30-45 

55-80 
15-30 

While  conformity  with  any  of  these  classes  cannot  well  be 
determined  by  the  Inspector  it  may  frequently  be  his  duty 
to  locate  available  local  deposits  of  suitable  material,  in 
which  case  he  should  be  familiar  with  a  few  simple  field 
tests  to  serve  as  a  guide  in  distinguishing  between  the  good 
and  the  bad. 

144.  Field  Tests  of  Materials,  (a)  When  inspecting 
available  local  deposits  of  sand  or  sandy  soil,  it  should  be 
remembered  that  a  hard  coarse  angular  sand  free  from  mica 


106         Sand-clay,  Gravel,  Shell,  or  Slag 

is  most  desirable  in  order  to  obtain  an  interlocking  of  the 
grains  under  compaction,  thus  producing  considerable  me- 
chanical stability  when  the  grains  are  held  together  with 
a  clay  binder.  Visual  examination  and  the  use  of  a  10- 
and  50-  or  60-mesh  sieve  (§371)  will  be  found  useful  when 
comparing  various  products.  Only  that  portion  passing 
the  10-mesh  sieve  should  receive  consideration  from  the 
standpoint  of  a  possible  sand-clay  mix.  If  much  mica  is 
present  the  product  should  be  discarded  as  inferior,  as 
even  a  small  per  cent  of  mica  seriously  interferes  with  the 
interlocking  of  the  sand  grains. 

(6)  Clays  or  clayey  soils  should  be  examined  for  their 
plasticity,  resistance  to  slaking  and  freedom  from  mica. 
Relative  plasticity,  which  is  a  measure  of  cementing  value, 
may  be  determined  by  mixing  the  clay  with  water  to  the 
consistency  of  stiff  dough  and  noting  if  the  product  may  be 
easily  worked  into  shapes  which  it  will  retain  without 
crumbling.  Resistance  to  slaking  is  ascertained  by  sun- 
drying  the  molded  shapes,  then  placing  them  under  water 
and  noting  whether  the  product  sloughs  down  slowly  or 
rapidly.  A  slow-slaking  product  is  preferable  to  one  which 
slakes  rapidly. 

(c)  The  relative  suitability  of  natural  sand  clays  and  top- 
soils  is  indicated  by  mixing  them  with  water  to  the  con- 
sistency of  stiff  dough  and  molding  them  into  small  spheres 
of  approximately  the  same  size.  The  spheres  should  be 
allowed  to  thoroughly  sun-dry  and  then  examined  for 
shrinkage,  which  is  an  undesirable  characteristic  manifested 
by  the  development  of  cracks.  The  spheres  should  next  be 
placed  in  a  shallow  pan  and  covered  with  water  which 
should  be  poured  in  gently.  Under  this  test  rapid  slaking 
indicates  an  undesirable  product.  If  it  is  desired  to  ascer- 
tain the  best  combination  of  sand  and  clay,  a  number  of 
mixtures  of  the  available  materials  should  be  made,  varying 
from  equal  parts  of  sand  and  clay  to  six  parts  of  sand  and 
one  part  of  clay.  These  mixtures  should  be  made  into 


Sand-Clay  and  Topsoil  Roads  107 

pastes,  molded  and  tested  for  shrinkage  and  resistance  to 
slaking  as  described  above.  A  record  should  be  made  for 
each  mixture  and  care  should  be  taken  that  the  specimens 
are  properly  identified,  by  means  of  marks,  for  the  shrink- 
age test,  and  relative  position  in  the  pan,  during  the  slaking 
test.  In  addition  to  the  characteristics  of  nonshrinkage  and 
resistance  to  slaking,  both  natural  and  artificial  mixtures 
should  feel  distinctly  gritty  when  rubbed  between  the  hands. 
145.  Measurements.  Depending  upon  the  method  of 
construction  which  is  to  be  followed  as  well  as  upon  local 
custom,  measurement  and  payment  may  be  made  upon  the 
basis  of  cubic  yards  of  surfacing  materials  used,  measured 
in  excavation,  loose  spread,  or  after  compaction.  In  any 
event  the  Inspector  may  be  required  to  measure  depth  and 
width  and  at  times  length.  When  the  work  is  paid  for  on 
the  arbitrary  basis  of  cubic  yards  in  accordance  with  a 
typical  cross  section  of  the  road,  the  computation  of  quan- 
tity is  a  simple  matter.  If  paid  for  on  the  basis  of  cubic 
yards  of  material  delivered  and  excavated  from  the  roadbed, 
measurements  of  loose  material  in  place  or  before  placing 
may  be  required.  This  method  is  not  exceedingly  accurate, 
as  the  volume  of  loose  earth  is  not  a  constant  (§  48c, 
§  50c).  In  general,  however,  a  loose  sand-clay  mixture  will 
compact  to  about  two  thirds  of  its  original  volume,  which 
means  that  a  loose  depth  of  approximately  12  inches  will  be 
required  to  produce  a  compacted  depth  of  8  inches.  Three 
cubic  yards  loose  is  then  equal  to  two  cubic  yards  compacted. 
Upon  this  basis  Fig.  15  shows  the  cubic  yards,  loose  measure, 
required  to  construct  each  100  linear  feet  of  road  8  inches 
thick  for  various  widths.  When  it  is  necessary  to  mix 
either  sand  or  clay  with  the  original  soil,  the  required 
depth  of  plowing  of  the  original  soil  is  also  indicated.  In 
this  diagram  a  uniform  compacted  depth  of  8  inches  is 
assumed.  For  10  inches  compacted  thickness  all  values 
should  be  multiplied  by  1.25,  and  for  12  inches  compacted 
thickness,  by  1.5. 


108         Sand-clay,  Gravel,  Shell,  or  Slag 

If  a  greater  thickness  is  specified  for  the  center  than  for  the 
sides  of  a  road,  the  values  should  be  multiplied  by  a  factor 
determined  by  dividing  the  actual  end  section  area  by  one 
for  the  same  width  8  inches  thick  (§  360) .  While  this  dia- 
gram will  be  found  useful  if  properly  applied,  it  should  be- 
remembered  that  the  values  are  only  approximate  as  the 
120 


12  16  20  24 

WIDTH  OF  ROAD.  FEET 

Fig.     15     Quantities  of  Material  Required  for  Sand-clay  Construction 

presence  of  moisture  in  soil  may  produce  marked  differ- 
ences in  volume  as  compared  with  the  dry  soil. 

146.  Sampling,  (a)  Sand  and  clay,  natural  sand-clay 
and  topsoil  should  be  sampled  (§§  59  -  60)  prior  to  use, 
and  samples  of  the  final  mixture  before  consolidation  should 
also  be  taken  at  frequent  intervals  and  tested  prior  to  final 
acceptance  of  the  work.  Each  sample  submitted  to  the 
laboratory  should  weigh  approximately  10  pounds  and 


Sand-Clay  and  Topsoil  Roads  109 

should  be  shipped  in  a  tightly  covered  pasteboard  box,  can 
or  close-woven  cloth  bag. 

(6)  Preliminary  samples  from  the  roadbed,  if  the  original 
soil  is  to  serve  as  one  constituent  of  the  mix,  should  be  taken 
for  a  depth  of  approximately  8  inches  every  500  feet  of 
length.  Bank  deposits  of  sand  or  clay  to  be  carried  onto 
the  road  should  be  sampled  in  the  usual  manner  (§  60c). 
For  each  acre  or  less  of  topsoil  two  samples  should  be  taken, 
one  a  local  sample  from  the  center  of  the  area,  and  the 
other  a  composite  sample  produced  by  mixing  samples  taken 
from  a  number  of  points  in  the  area  at  least  50  feet  apart. 
Samples  of  topsoil  are  usually  taken  for  a  depth  of  8  inches, 
but  this  will  depend  upon  the  apparent  thickness  of  the  soil. 
All  samples  should  be  labeled  so  as  to  show  the  exact  loca- 
tion from  which  they  were  taken. 

(c)  After  the  mixture  has  been  spread  or  prepared  upon 
the  road  a  sample  should  be  taken  for  each  500  feet  of 
length  and  its  exact  location  recorded  as  an  item  for  identi- 
fication. Additional  samples  should  be  taken  at  any  point 
where  reason  exists  for  believing  the  mix  to  be  unsatisfactory. 

147.  Inspector's  Equipment.  Any  or  all  the  following 
equipment  may  be  needed  by  the  Inspector : 

For  measurements, 
A  50-foot  steel  tape, 
A  pocket  rule  (§  387). 

For  sampling : 

A  spade  and  possibly  a  pick  for  sampling  natural  deposits. 
A  garden  trowel  for  sampling  on  the  road. 
A  supply  of  close-woven  cloth  bags  about  12  inches 

long  and  6  inches  wide. 
A  ball  of  stout  twine. 

A  supply  of  blank  eyelet  tags  for  identification  informa- 
tion. 

For  testing: 

A  shallow  pan  about  10  inches  in  diameter. 


110         Sand-clay,  Gravel,  Shell,  or  Slag 

A  10-mesh  and  a  50-  or  60-mesh  field  sieve  (§  371). 
A  spring  balance  with  pan  capacity  of  200  grams  (§  371). 
For  records  and  reports : 
A  field  diary  and  pencil. 
A  supply  of  report  forms  (§  404) . 
A  carbon  paper  for  duplication  of  reports. 


GRAVEL  ROADS 

148.  General  Characteristics.  Gravel  roads  may  be 
composed  of  gravel  as  obtained  from  a  natural  deposit 
(§  43),  or  of  the  product  screened  to  eliminate  certain  sizes, 
or  of  crushed  and  screened  pebbles.  The  last  mentioned 
type  is  similar  to  the  broken-stone  road  and  is  constructed 
in  the  same  manner  (§  1636).  When  the  product  is  not 
crushed  and  screened  it  should  be  considered  as  consisting 
of  two  principal  parts,  coarse  and  fine  aggregate,  both  of 
which  are  necessary  and  should  possess  certain  characteris- 
tic properties.  The  coarse  aggregate  or  material  that  will 
be  retained  on  a  J-inch  screen,  which  is  the  gravel  proper, 
should  predominate  and,  providing  the  natural  fine  aggre- 
gate possesses  the  proper  cementing  quality,  should  prefer- 
ably consist  of  pebbles  of  high  resistance  to  wear.  These 
pebbles  impart  mechanical  stability  to  the  road,  but  as 
they  are  usually  rounded  and  will  not  interlock,  must  be 
held"  in  place  by  the  fine  aggregate  which  will  pass  the 
J-inch  screen.  The  fine  aggregate  should  be  present  in  suf- 
ficient quantity  to  at  least  fill  the  voids  in  the  coarse  ag- 
gregate and  should  possess  considerable  cementing  value. 
Cementing  value  is  imparted  by  clay,  limestone  or  iron 
hydroxide.  When  the  binder  is  clay,  a  natural  sand-clay 
gravel  is  the  best  type  and  as  such  exhibits  the  characteris- 
tics of  a  sand-clay  road  (§  141),  except  that  it  possesses 
much  greater  mechanical  stability  or  resistance  to  dis- 
placement under  traffic.  An  excess  of  clay  or  of  sand  in  the 
fine  aggregate  produces  the  same  general  effect  as  in  a  sand- 


Gravel  Roads  111 

clay  road,  but  to  a  less  extent.  In  the  absence  of  clay,  iron 
hydroxide  serves  a  similar  purpose  in  certain  gravels.  If 
the  coarse  aggregate  is  limestone,  neither  clay  nor  iron 
hydroxide  need  be  present,  as  sufficient  calcareous  matter 
will  be  produced  by  abrasion  to  serve  as  a  cementing 
medium. 

149.  Construction  Methods.  A  gravel  road  may  be  laid 
directly  upon  a  graded  roadbed  or  in  a  trenched  roadbed 
in  one  or  more  courses.  No  course  should  have  a  finished 
depth  of  over  5  inches,  as  it  is  impractical  to  properly  con- 
solidate a  greater  thickness.  Courses  3  or  4  inches  thick 
after  compaction  are  to  be  preferred.  The  maximum  size 
pebble  which  is  permissible  for  each  course  should  be  speci- 
fied and  should  not  exceed  two-thirds  the  compacted  thick- 
ness. The  maximum  diameter  of  pebbles  in  the  top  or 
wearing  course  should  not  exceed  2  inches,  and  this  will 
frequently  necessitate  screening  the  gravel  before  use.  If 
there  is  a  deficiency  of  binding  material  in  the  gravel  a  rela- 
tively thin  layer  of  clay  is  sometimes  spread  over  each  course 
and  harrowed  in  before  the  course  is  compacted.  If  an 
excess  of  clay  is  present  sand  is  worked  into  the  gravel  in 
the  same  manner  for  the  purpose  of  obtaining  a  sand-clay 
void  filler  and  binder.  The  gravel  should  not  be  dumped 
on  the  road  in  piles  from  which  it  is  spread  out  by  flattening 
the  piles,  as,  even  after  harrowing  and  rolling,  uniform 
compaction  will  not  be  obtained  and  an  uneven  surface  will 
ultimately  develop.  The  use  of  spreading  wagons  is  to  be 
preferred.  After  spreading,  the  gravel  should  be  harrowed 
and  shaped.  Travel  is  sometimes  depended  upon  to  com- 
pact the  gravel,  but  the  use  of  a  roller  is  more  customary 
and  is  greatly  to  be  preferred.  When  the  cementing  material 
is  other  than  clay  the  road  should  be  sprinkled  just  prior  to 
compaction  and  in  very  dry  weather  a  light  sprinkling  may 
be  desirable  in  the  case  of  a  clay  binder.  After  being  opened 
to  traffic  the  road  should  be  watched  for  the  development  of 
depressions  or  raveling,  which  should  be  immediately 


112         Sand-clay,  Gravel,  Shell,  or  Slag 

remedied  by  the  addition  of  more  gravel  or  binder  and 
thorough  rolling. 

150.  Material  Requirements.  The  requirements  of  gravel 
for  a  gravel  road  must  of  necessity  be  limited  by  the  char- 
acteristics of  local  material.  Thus  when  clay  is  the*  binder, 
a  natural  sand-clay  gravel  is  to  be  preferred.  If  not  locally 
available,  however,  a  sand  gravel  or  a  clay  gravel  may  often 
be  used  to  advantage  if  its  admixture  with  the  proper  pro- 
portion of  the  missing  constituent  is  specified,  with  the  idea 
of  ultimately  securing  a  sand-clay  mixture  for  the  fine 
aggregate.  Specifications  frequently  require  that  the  true 
gravel  fragments  be  composed  of  hard  durable  rock  and 
sometimes  an  abrasion  test  (§  5 la)  requirement  is  included. 
Irrespective  of  the  type  of  cementing  material  the  minimum 
cementing  value  (§  52)  of  the  fine  aggregate  which  will  pass 
a  J-inch  screen  may  be  specified.  Certain  grading  require- 
ments are  very  desirable,  but  should  be  so  drawn  as  to 
allow  for  a  reasonable  range  of  grading.  Thus  the  maximum 
size  of  pebble  allowable  as  well  as  the  relative  proportion 
of  coarse  and  fine  aggregates  may  be  covered  by  requiring 
all  of  the  material  upon  test  to  pass  a  maximum  size  labora- 
tory screen  and  a  certain  minimum  and  maximum  amount 
to  be  retained  on  the  J-inch  screen.  Both  the  coarse  and 
the  fine  aggregates  may  further  be  required  to  show  an 
intermediate  grading.  As  an  example,  the  following  grad- 
ing requirements  for  gravel  for  wearing  course  is  briefed 
from  typical  specifications  of  the  U.  S.  Bureau  of  Public 
Roads : 

or  noqr;  bsbnoq^b '•••••  frftrfitomog  »«  hvfliT     :bf#$&$&1&(iii 
Entire  Gravel  Product  Per  cent 

Passing  2-inch  screen,  not  less  than    ..  95 

Total  retained  on  J-inch  screen 50-75 

Coarse  Aggregate 

Total  retained  on  1-inch  screen 25—75 

Fine  Aggregate 

Total  passing  200-mesh  sieve 15-35 


Gravel  Roads  113 

Conformity  with  such  requirements  may  frequently  be  de- 
termined by  the  Inspector  and  certain  simple  field  tests 
may  be  employed  to  ascertain  the  general  character  of  the 
gravel  apart  from  its  grading. 

151.  Field  Tests  of  Materials,  (a)  When  locating  avail- 
able deposits  of  gravel  visual  inspection  is  of  considerable 
service  in  distinguishing  between  suitable  and  unsuitable 
products.  If  the  face  of  a  gravel  bank  is  exposed  and  the 
gravel  will  stand  on  a  practically  vertical  slope,  a  good  quality 
of  cementing  material  in  the  fine  aggregate  is  indicated.  If, 
on  the  other  hand,  the  face  crumbles  readily  and  develops 
considerable  slope  an  inferior  cementing  material  is  indi- 
cated. The  soundness  of  gravel  pebbles  may  be  roughly 
ascertained  'by  breaking  a  sufficient  number  with  a  small 
hammer.  An  examination  of  the  faces  caused  by  fracture 
may  enable  the  Inspector  to  identify  the  prevailing  rock 
groups  (§  16)  and  thus  obtain  an  idea  of  the  physical  char- 
acteristics which  the  coarse  aggregate  possesses.  Gravels 
containing  a  large  proportion  of  pebbles  which  break  readily, 
particularly  if  they  are  sandstone  pebbles,  will  prove  to 
possess  inferior  wearing  qualities.  With  a  little  care  in 
selection  and  the  use  of  a  suitable  spring  balance  (§  374)  the 
Inspector  will  be  able  to  determine  with  considerable  accu- 
racy the  relative  proportion  of  sound  and  unsound  pebbles 
in  a  gravel  which  is  composed  of  a  number  of  kinds  of  rock. 

(6)  The  grading  of  gravels  should  be  ascertained  and  the 
use  of  a  2-  or  3-inch  screen,  a  J-inch  screen  and  a  200-mesh 
sieve  (§  371)  will  be  found  of  most  value.  In  addition,  other 
screens  or  sieves  may  be  used  to  advantage  as  called  for  in 
the  gravel  specifications.  Before  discarding  a  gravel  as 
unsuitable  on  account  of  grading,  the  possibility  of  making 
it  suitable  by  admixture  with  another  product  such  as  clay 
or  sand  should  receive  consideration,  particularly  if  the 
specifications  allow  for  such  mixing. 

(c)  When  clay  is  the  binding  material  it  may  be  desirable 
to  test  the  fine  aggregate  as  for  sand-clay  mixtures  (§  144). 


114 


Sand-clay,  Gravel,  Shell,  or  Slag 

In  such  cases  a  10-mesh  and  a  50-  or  60-mesh  sieve  will  be 
needed  in  addition  to  those  previously  mentioned. 

152.  Measurements,     (a)  In  the  construction  of  a  gravel 
road,  the  gravel  is  usually  paid  for  on  the  basis  of  square 


fi    TO 


28 


12  16  20  24 

WIDTH  OF  ROAD.  FEET 

Fig.  16     Cubic  Yards  of  Gravel  Required  for  Gravel 
Road  Construction 

yards  or  of  cubic  yards  of  finished  gravel  roa'd.  In  such 
cases,  measurements  of  depth,  width  and  length  of  com- 
pacted material  should  be  made  by  the  Inspector.  If 
specifications  have  been  followed  the  quantity  of  material 
per  unit  length  will  then  be  determined  by  multiplying  such 


Gravel  Roads 


115 


length  by  the  area  of  the  end  section  as  shown  on  the  plans 
(§  360).  Sometimes,  however,  gravel  is  paid  for  on  the 
basis  of  cubic  yards  or  tons  delivered  on  the  work.  Measure- 
ment may  then  be  required  in  wagons  (§  364)  or  deposited 


100 


POUNDS  PER  CU.  FT.  LOOSE 
105  110  115 


27  28  29  30  3i  32 

HUNDRED  POUNDS  PER  CU.  YD,  LOOSE 
Fig.  17    Tons  of  Gravel  Required  for  Gravel  Road 
Construction 

loose  upon  the  road.    In  addition,  the  gravel  may  sometimes 
be  measured  in  excavation  (§  362) . 

(6)  As  used  in  gravel-road  construction,  gravel  may  weigh 
from  2700  to  3300  pounds  per  cubic  yard,  and  will  shrink 
from  20  to  30  per  cent  from  loose  spread  to  compacted  con- 


116         Sand-clay,  Gravel,  Shell,  or  Slag 

dition.  A  shrinkage  of  at  least  25  per  cent  is  ordinarily 
figured  upon  when  loose  measurement  is  made.  This  means 
that  when  estimating  the  quantity  of  loose  material  delivered 
from  measurements  of  compacted  thickness  the  compacted 
volume  should  be  increased  by  one  third.  Upon  this  basis, 
the  diagrams  shown  in  Figs.  16  and  17  may  be  of  service 
to  the  Inspector  in  connection  with  measurements  which  he 
is  called  upon  to  make.  It  should  be  remembered,  however, 
that  these  values  are  only  approximate  owing  to  the  fact 
that  shrinkage  by  compaction  will  depend  not  only  upon 
the  exact  grading  of  the  gravel  but  upon  the  effect  of  mois- 
ture in  the  fine  aggregate  (§  48c,  §  50c). 

If  measurement  and  purchase  are  based  upon  the  weight  of 
material  it  may  be  necessary  for  the  Inspector  to  determine 
the  weight  of  the  gravel  per  cubic  yard  or  cubic  foot  (§  375). 
Figure  17  shows  the  number  of  tons  per  100  square  yards  of 
surface  for  different  compacted  depths  and  for  different 
weights  per  cubic  yard  or  cubic  foot,  loose  measure. 

153.  Sampling.  Gravel  should  be  sampled  (§  59,  60) 
prior  to  its  acceptance  and  during  use.  Each  sample  sub- 
mitted to  the  laboratory  should  in  most  cases  weigh  not  less 
than  50  times  the  weight  of  the  largest  fragment  present. 
The  following  will  serve  as  a  general  guide  for  use  in  this 
connection : 

Above  2  inches  in  diameter 60  to  75  Ib. 

Two  inches  maximum  diameter 40  " 

One  and  one  half  inches  maximum  diameter. ;  20  " 

One  inch  or  less  maximum  diameter T7""*  10  " 

Samples  should  be  shipped  in  tight  wooden  boxes  or  close- 
woven  cloth  bags. 

(6)  Preliminary  samples  from  natural  deposits  (§  60j) 
should  be  taken  as  far  in  advance  of  acceptance  or  rejection 
as  practicable.  If  other  than  grading  tests  are  required,  at 
least  10  days  should  be  allowed.  During  use  a  sample  should 
be  taken  and  tested  for  grading  by  the  Inspector  from  each 


Shell  Roads  117 

bulk  shipment  (§  60c)  and  if  hauled  in  wagons  he  should 
test  at  least  one  sample  for  every  1000  linear  feet  of  road. 
More  frequent  sampling  and  testing  will  be  advisable  if  the 
material  appears  to  vary  considerably  in  grading.  When 
laboratory  tests  for  quality  (§  60a)  are  specified,  a  sample 
should  be  shipped  to  the  laboratory  for  each  mile  of  road 
or  when  the  quality  of  the  product  being  furnished  appears 
to  vary  markedly  in  quality. 

154.  Inspector's  Equipment.  Depending  upon  specifica- 
tion requirements  and  the  importance  of  the  work,  the 
Inspector  will  require  any  or  all  of  the  following  equipment: 

For  measurements : 

1  50-foot  steel  tape. 

A  pocket  rule  (§  387). 
For  sampling: 

A  pick  and  shovel  for  sampling  natural  deposits. 

A  supply  of  close-woven  cloth  bags  of  suitable  size. 

A  ball  of  stout  twine. 

A  supply  of  eyelet  tags  for  identification  information. 
For  testing: 

A  geologist's  hammer  for  breaking  pebbles. 

A  set  of  field  screens  and  sieves  with  openings  of  3", 
2",  1|",  I",  \"  and  200-mesh.  A  10-mesh  and  a  50-or 
60-mesh  sieve  may  also  be  found  of  service  (§371). 

A  spring  balance  with  pan  capacity  of  10  pounds  and 
for  clay  binder  gravels  one  with  pan  capacity  of  200 
grams  will  also  be  found  useful  (§371). 
For  records  and  reports: 

A  field  diary  and  pencil. 

A  supply  of  report  forms  (§  404). 

A  carbon  paper  for  duplication  of  reports. 

SHELL  ROADS 

155.   General  Characteristics.    Shell  roads  are  constructed 
like  gravel  roads  (§  149)  in  one  or  more  courses.    All  shells 


118         Sand-clay,  Gravel,  Shell,  or  Slag 

are  composed  mainly  of  calcium  carbonate  and  as  they  crush 
easily  under  compaction  produce  sufficient  fine  aggregate 
to  fill  the  voids  between  and  bind  together  the  larger  frag- 
ments of  shell.  While  the  shells  are  sometimes  spread  loose 
and  allowed  to  compact  and  bond  under  traffic  better  prac- 
tice calls  for  shaping  and  rolling  with  the  use  of  water  and  a 
light  covering  of  sand  or  sandy  soil.  Oyster  and  clam  shells 
are  most  commonly  employed  and  may  be  washed  or  un- 
washed. If  the  latter,  they  are  sometimes  called  mud  shells 
owing  to  the  accumulation  of  earthy  material  which  they 
hold  after  being  dredged.  Clean  shells  are  often  obtained 
in  quantity  from  canneries. 

156.   Inspection.     Besides  visual  inspection  of  quality  and 
usual  attention  to  construction  details,  the  Inspector  should 


5000 


fc 

£4000 


g  3000 


2000 


1000 


16  20  24 

WIDTH   OF  ROAD,  FEET 


28 


Fig.  18    Bushels  of  Clean  Oyster  Shells  Required  for 
Shell  Road  Construction 

make  necessary  measurements  of  material,  as  in  the  case  of 
gravel  (§  152).    He  will  seldom  be  required  to  take  samples. 


Maintenance  119 

Clean  shells  shrink  to  about  one  half  their  loose  volume 
under  compaction  and  are  sometimes  purchased  and  meas- 
ured upon  the  oyster  bushel  basis  of  If  cubic  feet  per  bushel. 
In  Maryland  the  weight  of  a  bushel  of  clean  oyster  shells 
is  set  at  57  pounds,  which  makes  1231  pounds  per  cubic  yard 
loose,  or  2462  pounds  compacted.  Upon  this-basis,  Fig.  18 
shows  the  number  of  bushels  loose  required  to  construct 
100  linear  feet  of  compacted  road  of  various  widths  and 
depths.  To  translate  to  cubic  yards  per  100  linear  feet, 
divide  the  values  in  bushels  by  21.6  or  use  Fig.  45  by  doub- 
ling the  values  for  the  desired  thickness. 

SHOVEL-RUN   OR  CRUSHER-RUN  SLAG  ROADS 

157.  General  Characteristics.     Shovel-run  or  crusher-run 
slag  should  be  considered  on  the  same  general  plane  as  gravel 
roads  (§§  148,  149).    Blast-furnace  slag  (§  168)  is  commonly 
used  as  dug  from  slag  banks  with  a  steam  shovel.    Some- 
times   the    product    is    crushed    and    screened   to    remove 
undesirably  large  fragments  before  it  is  placed  upon  the 
roadbed.     The  cementing  material  is  fine  slag  dust  origi- 
nally present  and  also  produced  during  compaction. 

158.  Inspection.     Material  requirements,  field  tests,  meas- 
urement,   sampling,    and   inspectors   equipment   are   much 
the  same  as  for  gravel  roads  constructed  of  a  limestone 
gravel  (§§  150-  154).     A  minimum  weight  per  cubic  foot  is 
often  specified,  however,  and  the  Inspector'  may  be  required 
to  determine  weight  per  cubic  foot  (§  375)  and  make  use  of 
such  determination  in  estimates  of  quantities. 

MAINTENANCE 

159.  General  Methods.    The  maintenance  of  sand-clay, 
gravel,  shell,  and  shovel-run  slag  roads  consists  in  filling  ruts 
and  depressions  with  fresh  material  as  used  in  the  original 
construction.    Frequently  it  is  necessary  to  reshape  the  road 


120          Sand-clay,  Gravel,  Shell,  or  Slag 

by  means  of  a  drag.  When  the  road  is  badly  out  of  shape 
it  may  be  necessary  to  scarify  and  harrow  the  surface  to 
suitable  depth,  shape  the  loose  material  with  a  road  machine 
or  drag,  cover  with  an  additional  thickness  of  new  material 
and  consolidate  the  road  as  in  original  construction. 

160.  Inspection.  Inspection  of  maintenance  should  con- 
sist in  seeing  that  the  methods  specified  are  followed  and 
that  the  characteristics  of  the  materials  used  are  as  required. 
Measurements  should  be  made  as  for  construction  work. 
The  extent  of  sampling  and  testing  will  depend  upon  the 
amount  of  work  and  materials  involved  in  the  maintenance 
contract,  but  in  general  should  be  similar  to  that  required 
for  construction. 

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CHAPTER  VIII 

INSPECTION  OF  BROKEN-STONE  AND 
BROKEN-SLAG  ROADS 

GENERAL   CHARACTERISTICS 

161.  Definition.     Broken-stone  roads  or   pavements   are 
those  constructed  with  rock  which  has  been  artificially  broken 
or  crushed  into  irregular  angular  fragments  and  separated 
into  sizes  or  commercial  grades,  each  grade  containing  a 
preponderance  of  fragments  with  certain  ranges  of  diameter. 
Such  products  may  be  manufactured  from  massive  rock, 
field  stone,  boulders  or  gravel.    Broken-slag  roads  are  con- 
structed with  products  produced  in  the  same 'manner  from 
slag.     When  no  separation  of  sizes  is  made  and  the  output 
of  the  crusher  is  used  directly  in  construction,   the  road 
should  be  termed  a  crusher-run  stone  or   crusher-run   slag 
road  (§  157),  to  distinguish  it  from  one  which  has  been  con- 
structed of  a  number  of  sizes  or  grades  of  material.     When 
a  crusher-run  product  is  used,  the  methods  of  construction 
and  inspection  are  similar  to  those  described  under  Gravel 
Roads  (§  149). 

162.  Types.     There  are  two  principal  types  of  broken- 
stone  roads  commonly  designated  as  T3lford  and  Macadam. 
Use  of  the  Telford  type  is  largely  confined  to  the  construc- 
tion of  foundations  in  cases  where  the  natural  subgrade  or 
soil  conditions  are  poor  and  the  traffic  heavy.    The  Telford 
road  or  foundation  is  composed  of  large  stone  fragments 
napped  to  approximately  rectangular  shape  and  set  close 
together  by  hand.     The  interstices  are  filled  with  smaller 
fragments  which  are  wedged  into  place  by  rolling  or  tamping. 

121 


122     Broken-Stone  and  Broken-Slag  Roads 

The  Macadam  type  is  composed  of  one  or  more  courses  of 
a  definite  size,  crushed  or  broken  product  in  which  the  frag- 
ments are  interlocked  by  compaction  and  in  which  the  sur- 
face course,  at  least,  is  filled  with  fine  mineral  particles  and 
bound  together  by  sprinkling  with  water  and  rolling.  The 
term  Telford-macadam  is  frequently  applied  to  a  Macadam 
road  with  a  Telford  foundation. 

163.  General  Methods  of  Construction,  (a)  In  the  Tel- 
ford  road  or  foundation  the  stones  should  be  laid  on  the  sub- 
grade  in  parallel  courses  with  the  broadest  face  down  when 
their  specified  dimension  for  depth  is  perpendicular  to  the 
surface.  They  should  be  placed  so  as  to  break  joints  and 
wedged  into  position  by  driving  into  the  interstices  small 
stone  fragments  of  suitable  size.  All  projecting  points  should 
be  napped  off,  the  surface  voids  filled  with  small  stone  and 
the  road  thoroughly  compacted  by  rolling  with  a  three- 
wheel  roller  weighing  not  less  than  10  tons.  If  very  irregular, 
the  large  stone  should  be  napped  into  approximately  rect- 
angular pieces  before  laying..  A  depth  of  8  inches  after 
napping  is  usually  specified,  while  a  width  of  from  2  to  6 
inches  and  a  length  of  from  6  to  12  inches  may  be 
allowed. 

(6)  In  the  Macadam  road  a  specified  size  (§  17 c)  of  broken 
stone  or  slag  is  first  spread  on  the  roadbed  to  such  depth 
that  after  compaction  it  will  have  the  desired  thickness. 
It  is  then  rolled  until  the  fragments  interlock  and  may 
afterwards  be  filled  with  screenings,  sand,  or  sandy  soil 
which  is  spread  and  rolled  or  broomed  into  the  voids.  As 
this  course  serves  as  a  foundation,  the  void-filling  material 
is  sometimes  omitted,  but,  if  used,  all  excess  should  be  re- 
moved from  the  surface  before  the  next  course  of  stone  is 
spread.  A  second  course  of  stone  which  is  also  of  specified 
size  is  then  spread,  interlocked  by  rolling,  and  filled  with 
screenings,  after  which,  if  it  is  to  serve  as  a  wearing  course, 
the  road  is  well  sprinkled  and  rolled  until  bonded  with  the 
addition  of  a  thin  course  of  screenings  which  remains  on 


Important  Details  of  Macadam  Construction  123 

the  surface.  The  second  course  is  sometimes  followed  by 
a  third  or  wearing  course,  in  which  case  it  is  constructed 
in  the  same  manner  as  the  foundation. 


IMPORTANT  DETAILS   OF  MACADAM 
CONSTRUCTION 

164.  Preparation  of  Subgrade.  The  subgrade  is  usually 
prepared  as  a  shallow  trench  of  the  same  width  as  the  broken- 
stone  surface.  It  is  commonly  protected  by  earth  or  gravel 
shoulders,  but  in  the  case  of  city  streets  its  sides  may  be  curbs 
or  gutters.  It  is  very  important  that  the  subgrade  be 
brought  to  true  line  and  grade  when  thoroughly  compacted. 
Bumps,  depressions,  or  ruts  in  the  subgrade  will  almost 
invariably  appear  in  the  surface  of  the  finished  road.  The 
subgrade  should  be  firm  and  unyielding,  so  as  to  possess 
good  and  uniform  bearing  capacity  and  prevent  the  first 
course  of  broken  stone  from  being  driven  deeply  into  it.  A 
natural  sand-clay  or  gravelly  (§  141)  soil  makes  the  best 
type  of  subgrade.  If  of  a  clayey  nature  it  may,  therefore, 
be  improved  by  the  addition  of  sand  and  if  too  sandy  by  the 
addition  of  clay.  After  preparation  the  subgrade  should 
be  kept  in  such  condition  as  to  drain  readily,  and  all  soft 
and  yielding  material  which  will  not  readily  compact  when 
rolled  or  tamped  should  be  removed  and  replaced  with 
suitable  material.  It  should  preferably  be  rolled  with  a 
three-wheel  roller  weighing  not  less  than  10  tons  until  no 
further  compaction  can  be  obtained.  Sometimes  flat- 
headed  spuds  are  set  on  the  rear  wheels  of  the  roller  and  this 
aids  greatly  in  obtaining  maximum  compaction  if  rolling  is 
continued  until  the  spuds  make  little  or  no  impression  in  the 
surface  and  the  roller  wheels  ride  practically  clear.  When 
the  compacted  depth  of  broken  stone  is  to  be  the  same  for 
the  entire  width  of  road,  the  subgrade  carries  the  same 
crown  as  the  finished  road.  If  the  depth  of  stone  is  to  be 
greater  in  the  center  than  at  the  sides,  the  subgrade  may  be 


124     Broken-Stone  and  Broken-Slag  Roads 

flat  or  may  carry  less  crown.  In  certain  cases,  such  as  the 
construction  of  a  V-drain  foundation,  the  subgrade  will  be 
dished  or  carry  an  inverted  crown. 

165.  Spreading  the  Stone  or  Slag,  (a)  The  first  course 
of  broken  stone  should  never  be  allowed  to  be  spread  upon 
a  wet  and  spongy  subgrade  nor  on  one  which  is  rutted. 
Stone  which  has  been  spread  under  such  conditions  should 
be  removed  and  the  subgrade  condition  remedied.  The 
stone  should  not  be  dumped  in  piles  upon  the  subgrade  or 
foundation  and  spread  from  such  piles,  as  uniform  compac- 
tion cannot  then  be  secured,  owing  to  the  fact  that  at  the 
spot  originally  occupied  by  each  pile  the  compaction  before 
rolling  is  much  greater  than  the  immediate  surrounding 
area.  A  bumpy  surface  condition  will,  therefore,  ultimately 
result.  The  stone  as  delivered  may  be  dumped  upon  dump- 
ing boards  from  which  it  is  spread  by  shoveling  or  it  may  be 
shoveled  from  piles  dumped  along  the  side  of  the  road,  in 
which  case  caie  should  be  taken  that  it  does  not  first  become 
mixed  with  dirt  or  foreign  materials.  Properly  designed 
spreading  dump  wagons  may  also  be  used  to  place  the  stone 
directly  on  the  road  as  it  is  delivered.  Such  wagons  are 
fitted  with  wide  tires  and  bottoms  hinged  to  the  sides  or  ends 
so  that  by  partially  opening  the  bottom  the  stone  is  allowed 
to  run  out  upon  the  road.  It  may  then  be  spread  uniformly 
over  the  surface  by  means  of  forks.  If  at  any  time  the 
subgrade  material  should  become  churned  up  or  mixed  with 
the  foundation  course,  such  mixture  should  be  removed 
and,  after  remedying  the  subgrade,  should  be  replaced  with 
fresh  stone.  Care  should  always  be  exercised  to  see  that 
segregation  of  sizes  of  a  broken-stone  product  does  not 
occur  during  spreading. 

(6)  Screenings  should  be  spread  by  shoveling  from  piles 
along  the  side  of  the  road  or  from  dumping  boards.  In  order 
to  secure  a  uniform  covering  of  screenings  they  should  be 
thrown  from  the  shovel  with  a  side  swing  so  as  to  dis- 
tribute each  shovelful  over  a  considerable  area.  This 


Important  Details  of  Macadam  Construction  125 

will  prevent  the  screenings  from  caking  in  piles  upon  the 
surface. 

166.  Compacting  and  Bonding  the  Courses,  (a)  The 
foundation  and  intermediate  course,  if  constructed,  may 
be  compacted  and  bonded  in  exactly  the  same  manner  as 
the  wearing  course,  but  sometimes  the  use  of  screenings  is 
omitted  and  the  interlocking  of  the  large  stone  fragments 
only  is  depended  upon  to  produce  the  necessary  mechanical 
stability.  If  screenings  are  used,  all  excess,  after  filling  the 
voids,  should  be  broomed  from  the  surface  in  order  to  allow 
ithe  succeeding  course  to  tooth  in  and  form  a  continuous 
structure. 

(6)  After  spreading  the  large  stone,  each  course  should 
be  rolled  with  a  three-wheel  roller  weighing  not  less  than 
10  tons  until  the  fragments  interlock  and  do  not  creep  or 
wave  ahead  of  the  roller.  Rolling  should  begin  at  the 
extreme  edge,  overlapping  the  shoulder  on  the  surface 
course,  and  should  be  carried  parallel  to  the  center  line  of 
the  roadway.  Each  succeeding  trip  of  the  roller  should  uni- 
formly lap  the  preceding  rear  wheel  track  until  the  center 
line  of  the  road  has  been  reached,  after  which  rolling  should 
be  started  and  continued  from  the  other  edge  in  a  similar 
manner.  The  number  of  complete  rollings  required  to 
thoroughly  compact  a  course  will  depend  upon  the  thick- 
ness of  the  course  and  size  and  quality  of  stone.  It  is  dim- 
cult,  if  not  impossible,  to  satisfactorily  compact  a  loose 
thickness  of  over  six  inches  except  in  the  case  of  very  soft 
rock.  A  hard  tough  rock,  such  as  trap,  will  require  much 
more  rolling  than  a  relatively  soft  rock  such  as  limestone. 
If  rolling  is  carried  to  excess  the  sharp  edges  of  the  stone 
will  be  worn  away  and  the  fragments  become  rounded,  in 
which  case  satisfactory  interlocking  cannot  be  secured. 
This  feature  should  be  carefully  watched  by  the  Inspector. 
Until  the  coarse  stone  is  filled  or  covered  by  another  filled 
course,  no  traffic  other  than  that  necessary  to  bring  on  new 
stone  should  be  allowed  over  the  rolled  broken  stone. 


126     Broken-Stone  and  Broken-Slag  Roads 

(c)  Screenings  should  be  rolled  in  layers  just  sufficient 
to  cover  the  large  stone,  the  purpose  being  to  force  them 
into  the  voids  and  bind  the  coarser  fragments  together.  As 
they  are  thus  worked  into  the  voids  additional  screenings 
should  be  spread  until  no  more  can  be  forced  in.  The 
surface  should  then  be  well  sprinkled  with  water  and 
rolled,  the  operation  of  sprinkling  and  rolling  being  con- 
tinued until  a  slight  wave  of  grout  is  pushed  along  the  sur- 
face ahead  of  the  front  wheel  of  the  roller.  After  the  top 
course  is  compacted  and  puddled  in  this  manner,  it  should 
be  covered  with  a  thin  layer  of  screenings  and  allowed  to 
dry  out  before  being  opened  to  traffic. 


MATERIALS 

167.  Rock.  Rock  for  waterbound  broken-stone  roads, 
particularly  the  wearing  course,  should  preferably  possess 
good  resistance  to  abrasion  (§28),  high  toughness  (§29), 
and  high  cementing  value  (§  31).  As  a  matter  of  economy 
selection  is,  however,  generally  restricted  to  the  use  of  the 
most  available  rock  which  possesses  reasonably  satisfactory 
properties,  and  specifications  for  quality  usually  include 
only  a  percentage  of  wear  or  French  coefficient  of  wear 
requirement.  Experience  has  shown  that  certain  kinds  of 
rock  such  as  granite,  gneiss  (§  21),  sandstone,  quartzite 
(§  22),  schist,  shale,  and  slate  (§  26)  are  not  as  a  rule  suitable 
for  this  type  of  construction  and  their  use  is  frequently 
excluded  by  specifications.  The  Inspector  should,  therefore, 
be  able  to  identify  them.  Granite,  gneiss,  sandstone  and 
quartzite  are,  however,  sometimes  allowed  to  be  used  in 
the  lower  courses  and  even  in  the  wearing  course  if  lime- 
stone or  other  cementitious  screenings  are  used  for  binder. 
A  French  coefficient  of  7  is  usually  considered  a  minimum 
requirement  for  wearing  course  stone  and  5  for  foundation 
course.  For  heavy  traffic  roads  higher  limits  may  be  set 
if  the  rock  is  available.  Trap  rock  usually  possesses  desir- 


Materials  127 

able  qualities,  but  requires  considerable  traffic  to  produce 
sufficient  fine  material  by  abrasion  to  replace  the  original 
screenings  as  they  are  removed  from  the  surface  and  thus 
maintain  the  bond.  Unless  conditions  are  favorable  trap 
rock  roads  are,  therefore,  more  apt  to  ravel  than  those 
constructed  of  limestone,  which,  while  less  resistant  to  wear, 
possesses  a  higher  cementing  value.  Soft  limestone,  on 
the  other  hand,  will  produce  a  more  dusty  surface  in  dry 
weather.  Granites,  gneisses,  sandstones  and  quartzite  are 
usually  lacking  either  in  toughness  or  cementing  value.  In 
the  first  case,  the  larger  fragments  break  up  under  rolling 
and  traffic  and  in  the  latter  they  do  not  properly  bond  when 
puddled  and  rolled.  When  a  broken-stone  road  is  to  be 
covered  with  a  bituminous  mat  or  carpet  the  cementing 
value  of  the  rock  becomes  a  much  less  important  factor,  and 
due  allowance  for  this  fact  should,  therefore,  be  made  in 
specification  requirements. 

168.  Slag,  (a)  Slags  may  be  considered  as  artificial  rock 
resulting  as  a  by-product  in  the  reduction  of  metallic  ores. 
Their  chemical  or  mineral  composition  differs  materially 
from  that  of  rock,  however,  although  many  of  the  denser 
varieties  closely  resemble  natural  rock  in-  appearance  and 
structure.  Apart  from  composition,  the  physical  structure, 
and,  therefore,  the  physical  properties  of  slags  are  greatly 
influenced  by  conditions  under  which  they  are  allowed  to 
solidify  and  cool  from  their  original  molten  state.  If  these 
conditions  are  not  uniform,  slag  from  the  same  bank  may 
vary  from  a  hard,  tough,  dense  mass  to  a  porous  friable  prod- 
uct and  even  to  fine  dust.  Unless  exceptional  care  is  exer- 
cised in  the  production  of  broken  slag  for  highway  work, 
the  product  will  be  more  variable  in  quality  than  broken 
stone. 

(b)  The  slags  of  greatest  interest  in  road  construction 
at  the  present  time  are  those  produced  in  the  reduction  of 
iron  ore,  and  of  these  the  product  obtained  from  blast  fur- 
naces is  the  one  produced  in  greatest  quantity  and  most 


128    Broken- Stone  and  Broken- Slag  Roads 

widely  used.  Other  products,  such  as  open  hearth  iron 
slags  and  copper  or  lead  slags  are  sometimes  utilized,  but 
at  the  present  time  are  of  relatively  minor  importance. 
Most  blast-furnace  slags  are  rich  in  lime,  and,  therefore, 
possess  excellent  cementing  value.  They  usually  have  a 
semi-crystalline  structure  and  vary  from  light  to  dark  gray 
in  color.  Individual  fragments  frequently  show  a  large 
amount  of  glassy  material  and  a  more  or  less  porous  structure. 

(c)  As  used  in  highway  work,  blast-furnace  slags  are 
usually  obtained  from  large  banks,  where  they  have  been 
dumped  in  a  molten  or  semi-molten,  condition,  after  removal 
from  the  furnace,  and  allowed  to  slowly  air  cool.  Water 
cooling  or  any  other  rapid  method  is  apt  to  produce  a 
granular  or  porous  product.  Some  engineers  consider  it 
highly  desirable  that  the  slag  be  exposed  to  the  weather  and 
age  in  the  bank  a  considerable  period  in  order  to  allow  all 
rapid  disintegration  which  may  take  place  to  occur  before  it 
is  used,  and  specifications  sometimes  require  such  weathering. 
For  water-bound  roads,  the  physical  requirements  of  slag  are 
similar  to  those  specified  for  rock  except  that,  in  addition 
to  a  minimum  French  coefficient  of  wear  (§  28),  a  minimum 
weight  per  cubic  foot  is  also  commonly  specified.  The 
latter  property  may  have  to  be  determined  by  the  Inspector 
in  the  field  (§  375).  For  macadam  construction  a  minimum 
weight  of  as  low  as  55  or  60  pounds  per  cubic  foot  is  some- 
times set.  In  addition,  the  slag  may  be  required  to  show  a 
reasonably  uniform  density  and  quality  and  freedom  from 
metallic  iron.  Slag  banks  are  usually  excavated  by  means 
of  a  steam  shovel  and  the  slag  is  crushed  and  screened  in  the 
production  of  broken  slag  in  the  same  manner  as  rock  (§  17). 
The  shovel-run  or  crusher-run  product  is  sometimes  used 
directly  in  the  construction  of  roads  (§  157). 

169.  Sizes  of  Commercial  Products,  (a)  The  size  or 
grading  of  broken  stone  (§§  17c,  18c)  or  broken-slag  products 
used  in  waterbound  roads  is  a  matter  badly  in  need  of 
standardization  owing  to  unnecessary  variations  in  specifi- 


Materials  129 

cation  requirements  as  a  whole.     In  general,  fragments  of 
a  larger  size  are  required  for  the  foundation  than  for  the 
[wearing  course  proper,  although  in  the  case  of  soft  rocks 
,his  relation  is  sometimes  reversed  or  else  the  same  product 
s  used  for  both  courses.     It  is  usually  desirable  to  utilize 
as  nearly  as  possible  the  entire  output  of  the  crusher  from 
i  certain  size  down  and,  therefore,  to  use  the  individual 
izes  in  the  relative  proportion  that  they  are  produced. 
Three  and  sometimes  four  different  sized  products  are  fre- 
quently specified  when  the  road  is  to  be  built  from  founda- 
ion  up.     If  the  road  is  constructed  in  three  courses,  the 
same  size  product  is  frequently  used  for  two  of  the  courses. 
Ln  general,  the  maximum  size  of  fragment  should  not  exceed 
iwo  thirds  the  thickness  of  the  loose  course. 

(6)  As  an  illustration  of  size  and  grading  requirements 
'or  broken  stone  to  be  used  in  the  construction  of  a  two- 
course  road,  the  following  limits  from  typical  specifications 
of  the  U.  S.  Bureau  of  Public  Roads  may  be  cited.  These 
requirements  are  based  upon  actual  screen  tests  which  may 
made  in  the  laboratory  or  in  the  field  (§  371). 

Bottom- or  Foundation  Course  Stone  Per  cent 

Passing  3-inch  screen,  not  less  than 95 

Total  passing  2 J-inch  screen 25-75 

Retained  on  2-inch  screen,  not  less  than 85 

Top  Course  Stone 

Passing  2-inch  screen,  not  less  than 

Total  passing  If -inch  screen 25-75 

Retained  on  1-inch  screen,  not  less  than 85 

Screenings 

Passing  1-inch  screen 

Total  passing  J-inch  screen 

Such  products  may  be  obtained  by  the  utilization  of  a  com- 
mercial revolving  screen  with  sections  containing  circular 
openings  of  3",  2"  and  1"  in  diameter.  A  dust  jacket  may 
also  be  required  if  the  rock  is  soft  and  produces  an  excess  of 


130    Broken-Stone  and  Broken-Slag  Roads 

dust.  For  an  average  rock,  a  bottom  course  of  5  inches  and 
a  wearing  course  of  3  inches  in  thickness  will  utilize  prac- 
tically the  entire  output  of  a  crusher  and  provide  sufficient 
screenings  to  properly  bond  the  surface  with  a  slight  excess 
of  screenings,  in  the  case  of  the  softer  grades  of  rock,  which 
may,  if  desired,  be  used  in  filling  the  bottom  course.  For 
a  foundation  course  or  for  the  construction  of  the  entire 
road,  in  case  it  is  desired  to  have  large  fragments  in  the 
wearing  course,  the  entire  product  between  3"  and  1"  may 
be  used,  providing  each  course  is  at  least  4  inches  thick. 
In  such  case,  the  requirement  for  screenings  would  be  the 
same  and  for  coarse  broken  stone  or  broken  slag  as  follows: 

Per  cent 

Passing  3-inch  screen,  not- less  than 95 

Total  passing  2-inch  screen 25-75 

Retained  on  1-inch  screen,  not  less  than 85 

170.  Field  Tests,  (a)  The  Inspector  cannot  be  expected 
to  test  the  quality  of  rock  for  broken-stone  roads,  but  he 
should  be  able  to  identify  the  principal  rock  groups 
(§§  17-27)  and  be  familiar  with  their  characteristic  proper- 
ties, especially  if  specifications  eliminate  certain  rocks  by 
name.  The  rock  to  be  used  under  a  given  contract  is  usually 
approved  upon  laboratory  tests  made  in  advance  of  the 
work,  in  which  case  the  Inspector  will  find  it  convenient  to 
secure  a  specimen,  from  the  sample  tested,  to  visually  com- 
pare with  material  furnished  on  the  job.  In  the  case  of  slag 
products,  which  usually  show  a  greater  variation  in  appear- 
ance and  characteristics  of  individual  fragments,  a  compari- 
son sample  is  of  little  service,  but  determinations  of  weight 
per  cubic  foot  may  be  made  from  time  to  time  by  the  In- 
spector (§375)  to  ascertain  if  specifications  are  being  com- 
plied with  and  also  to  check  the  uniformity  of  the  product. 
Both  broken-stone  and  broken-slag  products  should  be 
watched  to  see  that  they  do  not  contain  an  excess  of  thin 
or  elongated  pieces,  disintegrated  or  weathered  fragments, 


Materials  131 

dirt  or  other  objectionable  material.  Any  filler,  other  than 
screenings,  which  is  allowed  to  be  used  should  not  become 
sticky  when  wet,  and  if  soil  is  used  it  should  be  examined  for 
this  characteristic  by  mixing  a  small  amount  with  water. 

(6)  The  size  or  grading  of  broken-stone  and  broken-slag 
products  should  be  determined  for  conformity  with  specifi- 
cation requirements,  and  a  set  of  selected  field  screens  (§371) 
from  the  maximum  diameter  to  J  inch  will  be  found  useful 
for  this  purpose. 

171.  Measurements,  (a)  Broken-stone  and  broken-slag 
roads  are  usually  measured  and  paid  for  on  the  basis  of 
square  yards  of  surface  in  place  which,  for  the  specified 
depth,  is  equivalent  to  a  compacted  cubic  yard  basis  with 
no  allowance  for  extra  thickness  or  material  lost  by  being 
forced  into  the  subgrade.  Measurements  of  length,  width, 
and  depth  of  compacted  material  should,  therefore,  be  made 
by  the  Inspector.  As  a  check  upon  this  and  also  when 
material  is  paid  for  upon  a  cubic  yard  or  ton  basis,  measure- 
ments of  loose  depth  and  of  quantities  by  volume  or  weight 
(§§  35-37)  of  material  in  cars  or  wagons  is  advisable.  In 
Telford  construction  the  actual  depth  of  the  large  stone 
should  be  measured  occasionally. 

(b)  Loose-spread  commercial  sizes  of  coarse  broken  stone 
or  broken-slag  products  contain  approximately  45  per  cent 
voids,  and  compacted  by  rolling  about  30  per  cent  voids 
(§  376) .  Shrinkage  from  loose  spread  to  compacted  thick- 
ness, therefore,  amounts  to  a  little  less  than  22  per  cent  or 
to  about  four  fifths  of  the  loose  depth.  This  means  that 
5  inches  of  loose-spread  rock  will  compact  to  about  4  inches. 
A  somewhat  greater  shrinking  will  result  if  the  stone  is  laid 
directly  upon  a  subgrade  which  is  not  composed  of  good 
material  thoroughly  compacted.  Theoretically,  about  0.3 
cubic  yard  of  compacted  filler  would  be  used  to  fill  the  voids 
in  one  cubic  yard  of  compacted  broken  stone,  and  this  would 
amount  to  somewhat  over  .37  cubic  yards  loose.  Filler  for 
foundation  or  intermediate  course  may,  however,  safely  be 


132    Broken -Stone  and  Broken -Slag  Roads 

assumed  as  not  over  .35  cubic  yards  loose  measure  for  each 
cubic  yard  of  compacted  broken  stone.  For  the  surplus  of 
screenings  allowed  to  remain  on  the  wearing  course,  about 


WIDTH  OF  ROAD,   FEET 
24  20  16 


12  16  2Q  24 

WIDTH  OF  ROAD,  FEET 


28 


Fig.  19     Quantity  of  Broken  Stone  Required  for 
Macadam  Construction 

.015  cubic  yards  loose  per  square  yard  of  surface  will  be 
required.  Upon  this  basis  Fig.  19  shows  the  number  of  cubic 
yards,  loose  measure,  of  coarse  stone  and  filler  or  screenings 


Materials 


133 


required  to  construct  100  linear  feet  of  various  widths  for 
compacted  courses  of  different  thickness. 


POUNDS  PER  CUBIC  FOOT 
80  70 


50 


60  70  80 

POUNDS  PER  CUBIC  FOOT 


Fig.  20     Quantity  of  Broken  Slag  Required  for 
Macadam  Construction 

As  applied  to  broken  stone  this  diagram  may  be  used  in 
connection  with  the  45  per  cent  void  curves  in  Figs.  4  and 
5  in  determining  the  number  of  tons  used  or  required,  provid- 
ing the  specific  gravity  of  the  rock  is  known.  Thus  the 


134    Broken -Stone  and  Broken -Slag  Roads 

number  of  cubic  yards  required  for  a  given  width  and  thick- 
ness, as  determined  from  Fig.  19,  multiplied  by  the  weight 
per  cubic  yard  of  rock,  as  obtained  from  the  45  per  cent 
void  curve  in  Fig.  4,  gives  the  weight  in  pounds  required 
for  the  same  width  and  thickness.  This  value  divided 
by  2000  then  gives  the  number  of  tons  required.  The 
same  result  may  be  secured  by  multiplying  the  value 
obtained  from  Fig.  19  by  100  and  dividing  the  result  by 
the  value  obtained  from  the  45  per  cent  curve  in  Fig.  5. 

(c)  In  the  case  of  slag,  if  measurement  or  purchase  is 
based  upon  the  weight  of  material  and  the  weight  per  cubic 
foot  (§  375)  or  cubic  yard  is  determined  by  the  Inspector, 
Fig.  20  may  prove  of  service.  In  this  figure  the  number  of 
tons  per  100  square  yards  of  surface  is  shown  for  different 
compacted  depths  and  different  weights  per  cubic  foot  loose 
measure.  It  will  ordinarily  be  found  that  slag  screenings 
weigh  more  per  cubic  foot  than  coarse  slag  from  the  same 
source,  owing  to  the  greater  density  of  the  small  fragments 
which  contain  less  air  pockets  than  the  larger  fragments. 

172.  Sampling,  (a)  Broken  stone  and  broken  slag  should 
be  sampled  (§§  38-40)  prior  to  and  during  use.  The  weight 
'of  each  sample  submitted  to  the  laboratory  for  tests  of 
quality  will  be  the  same  for  both  materials.  Size  or  grading 
tests  and  determinations  of  weight  per  cubic  foot,  if  re- 
quired, should  ordinarily  be  made  by  the  Inspector.  If 
the  Laboratory  requires  samples  for  such  tests,  however, 
the  weight  of  sample  for  each  product  to  be  tested  for  grad- 
ing-should  be  the  same  as  given  for  gravel  (§  153a).  For 
weight  per  cubic  foot  determinations  approximately  100 
pounds  will  be  needed.  Samples  should  be  shipped  in  tight 
wooden  boxes  or  heavy  burlap  bags.  For  size  or  grading 
tests  the  sample  bags  should  be  close  woven. 

(b)  Preliminary  samples  of  rock  from  the  quarry  or  crush- 
ing plant  should  be  taken  at  least  two  weeks  prior  to  accept- 
ance or  rejection.  Preliminary  samples  of  slag  should  be 
taken  from  the  crusher  or  that  portion  of  the  bank  which 


Maintenance  135 

it  is  proposed  to  use,  at  least  two  weeks  and  not  more  than 
one  month  prior  to  acceptance.  During  use  at  least  one 
sample  of  stone  or  slag  should  be  taken  and  tested  for  size 
by  the  Inspector  from  each  bulk  shipment  (§  40) .  If  hauled 
in  wagons  he  should  test  at  least  one  sample  for  every  1000 
linear  feet  of  road,  and  whenever  the  grading  of  a  product 
appears  to  vary  markedly.  Weight  per  cubic  foot  determi- 
nations, if  required,  should  be  made  when  sampling  for  size 
or  grading.  This  applies  to  each  size  of  product  covered  by 
the  specifications. 

MAINTENANCE 

173.  Methods,  (a)  The  cover  of  screenings  on  a  newly 
constructed  broken-stone  road  serves  only  as  a  temporary 
protection  for  the  top  course  while  the  latter  is  seasoning. 
This  cover  is  soon  removed  by  traffic  and  the  large  stones 
of  the  top  course  take  the  wear.  The  ideal  macadam  should 
produce  under  traffic  just  sufficient  fine  products  of  wear 
to  bond  the  larger  surface  fragments  and  replace  the  original 
filler  as  it  is  removed.  This  does  not  always  occur  and 
raveling  results,  together  with  the  formation  of  bumps  and 
depressions  if  the  material  of  which  the  road  is  built  is  not 
uniform  or  the  entire  road  has  not  been  constructed  uni- 
formly. In  the  first  case,  maintenance  may  consist  in  the 
treatment  of  a  road  for  the  purpose  of  retaining  the  neces- 
sary amount  of  fine  surface  material,  together  with  the  addi- 
tion of  screenings,  if  a  sufficient  amount  is  not  present  before 
treatment.  Frequent  sprinkling  with  water  during  dry 
periods  may  be  resorted  to  or  such  substances  as  calcium 
chloride  (§348),  concentrated  waste  sulphite  liquor  (§350), 
oil  or  tar  (§  182),  may  be  used  for  superficial  surface  treat- 
ment. If  a  mat  or  carpet  (§  183)  of  artificially  bound  fine 
aggregate  is  placed  upon  the  road  and  such  mat  removed 
as  it  wears  away,  the  coarse  stone  of  the  original  macadam 
is  not  subjected  to  external  wear,  so  that  the  original  ma- 
cadam is  not  maintained  as  such. 


136    Broken- Stone  and  Broken- Slag  Roads 

(b)  Holes,  depressions,  and  ruts  are  usually  remedied  by 
filling  with  fresh  material  similar  to  that  of  which  the  wear- 
ing course  is  constructed.     Such  material  should  be  com- 
pacted and  bonded  by  rolling  or  tamping  while  puddling 
with  water.     Unless  such  places  are  first  cut  out  so  as  to 
produce  excavations  with  approximately  vertical  sides  to 
a  depth  somewhat  greater  than  the  maximum  diameter  of 
stone  used  for  repairing,  the  repairs  are  apt  to  be  unsatis- 
factory, as  the  stone  will  tend  to  be  squeezed  out  under 
traffic.     Sometimes  repairs  are  made  with  the  addition  of  a 
cold  patching  bituminous  binder  such  as  emulsified  asphalt 
or  cut-back  tar  (§333). 

(c)  If  the  road  is  badly  out  of  shape  or  has  worn  away  to 
a  considerable  extent,  maintenance  may  consist  of  resurfac- 
ing.   If  a  new  surface  of  three  or  more  inches  of  loose  spread 
rock  is  to  be  constructed  and  the  old  road  surface  is  in 
reasonably  fair  condition,  the  stone  may  be  laid  directly 
upon  the  old  road,  from  which  all  excess  dirt  and  dust  have 
been  removed  by  brooming.    When  less  new  material  is  to 
be  added  or  the  original  road  is  badly  out  of  shape  it  should 
first '  be  lightly  scarified,  harrowed,   and   reshaped   with  a 
road  machine.    After  laying  the  new  stone,  all  of  the  loose 
material  is  then  compacted  and  bonded  as  in  original  con- 
struction. 

174.  Inspection.     Inspection   of  maintenance  should  be 
similar  in  character  to  that  required  for  construction.    The 
extent  of  sampling  and  testing  should   depend  upon  the 
amount  of  work  and  materials  involved.     When,  however, 
maintenance  involves   surface  treatment   with   bituminous 
or  other   materials,  additional  inspection   (§§  190-191)  will 
be  required. 

INSPECTOR'S  EQUIPMENT 

175.  Telford  Roads.     For  Telford  construction  the  fol- 
lowing equipment  is  all  that  the  Inspector  will  ordinarily 
require : 


Inspector's  Equipment  137 

For  Measurements: 
A  50-foot  steel  tape. 
A  pocket  rule  (§  387). 

For  Records  and  Reports: 
A  field  diary  and  pencil. 
A  supply  of  report  forms  (§  404) . 
A  carbon  paper  for  duplication  of  reports. 

176.  Macadam  Roads.  For  macadam  construction  the 
Inspector  will  require  the  same  equipment  as  for  Telford 
(§  175).  In  addition,  however,  he  should  be  provided  with 
any  or  all  of  the  following  equipment: 

For  Sampling: 

A  supply  of  burlap  or  close-woven  bags. 

A  ball  of  stout  twine. 

A  supply  of  eyelet  tags  for  identification  information. 

For  Testing: 

A  hand  sample  of  approved  rock  for  visual  comparison 

in  the  case  of  broken-stone  roads.     A  small  pocket 

magnifying  glass  will  also  frequently  prove  useful. 
A  set  of  field  screens  and  sieves  with  suitable  openings 

as  may  be  covered  in  specifications  for  size  (§  1696). 

Openings  of  3",  2",  H",  1"  and  \"  are  suggested  (§  371). 
A  spring  balance  with  pan  capacity  of  10  pounds  (§  371). 
A  cubic  foot  measure  for  determining  the  weight  per 

cubic  foot  of  broken  slag  (§  375). 


CHAPTER  IX 

INSPECTION  OF  BITUMINOUS 
SURFACE  TREATMENTS 

GENERAL  CHARACTERISTICS 

177.  Definition.     Bituminous  surface  treatment  consists 
in  the  superficial  application  of  bituminous  material  to  a 
road  surface  which  may  or  may  not  be  followed  with  a  rela- 
tively thin  covering  of  stone  or  slag  chips  or  screenings,  fine 
gravel,  sand  or  other  earthy  material.    Such  treatment  used 
in  completing  the  construction  of  bituminous  macadam  or 
bituminous  concrete  pavements  and  forming  an  essential 
part  of  such  construction  is  called  seal  coating  and  is  con-' 
sidered  under  these  types  of  pavements. 

178.  Types.     There    are    two    general   types    of   surface 
treatment,  that  in  which  the  material  is  applied  primarily 
as  a  dust  preventive  and  that  in  which  it  is  applied  pri- 
marily for  the  purpose  of  constructing  a  thin  bituminous 
mat  or  carpet  upon  the  road  surface.     In  the  latter  case, 
application  of  the  bituminous  material  is  followed  with  a 
cover  of  mineral  matter,  while  hvdust  prevention  this  cover 
is  usually  omitted.     The  use  of  a  dust  preventive  proper 
does  not  produce  a  new  wearing  surface,  but  merely  reduces 
the  formation  of  dust  and  tends  to  hold  in  place  the  fine 
material  on  the  road  surface.     The  old  road  surface,  how- 
ever, continues  to  take  the  wear  of  traffic.    When  a  bitumi- 
nous mat  or  carpet  is  constructed,  a  new  wearing  surface  is 
produced  which  itself  takes  the  direct  wear  of  traffic  and 
protects  the  underlying  original  road  surface.     Dust  pre- 
ventives are  used  in  treating  earth,  gravel,  shell,   broken 

138 


Important  Details  of  Surface  Treatment     139 

stone  and  slag  roads.  Carpeting  mediums  are  used  on  all 
of  these  but  the  earth  road  and,  in  addition,  sometimes  on 
Portland  cement  concrete  pavements.  Bituminous  carpets 
over  one  half  inch  thick  are  apt  to  shove  or  rut  under  traffic 
and  for  this  reason  the  rate  of  application  of  bituminous 
material  and  cover  should  be  carefully  covered  in  specifica- 
tions. 


IMPORTANT  DETAILS   OF  SURFACE  TREATMENT 

179.  Preparation  of  Road  Surface,  (a)  The  condition  of 
the  road  surface  just  preceding  application  of  a  bituminous 
material  is  an  extremely  important  matter  which  should 
be  given  close  attention  by  the  Inspector.  No  surface 
treatment  should  be  depended  upon  to  eliminate  ruts,  pot 
holes,  depressions,  bumps  or  waves  in  the  original  road. 
In  fact,  such  faults  are  more  apt  to  be  accentuated  by  sur- 
face treatment.  The  first  consideration,  therefore,  is  to 
see  that  all  surface  irregularities  in  the  road  are  remedied 
and  that  where  additional  stone,  slag,  gravel,  etc.,  are 
used  such  repairs  are  thoroughly  consolidated  before  the 
bituminous  material  is  applied.  In  some  cases  the  entire 
surface  may  have  to  be  reshaped  by  scarifying,  harrowing, 
bonding  and  rolling  before  surface  treatment  is  given.  In 
such  cases,  as  well  as  in  the  treatment  of  a  newly  constructed 
road,  it  is  advisable  to  let  the  finished  surface  season  for 
a  few  weeks  under  traffic  before  applying  the  bituminous 
material. 

(b)  The  second  important  detail  to  be  observed  is  that 
the  road  surface  is  as  clean  and  free  from  dust  as  possible. 
In  the  case  of  earth  roads,  little  can  be  done  other  than  to 
shape  and  consolidate  the  surface.  Broken-stone,  slag, 
gravel  and  shell  roads  should,  however,  be  broomed  to  re- 
move all  excess  fine  material,  care  being  taken  not  to  dis- 
turb the  bond  betwen  the  coarser  fragments.  When  the 
surface  is  well  bonded  a  mechanical  sweeper  may  often  be 


140          Bituminous  Surface  Treatments 

used  to  advantage,  but  such  sweeping  is  rough  and,  for  sur- 
faces more  readily  displaced,  hand  brooming  may  be  required. 
In  either  case,  the  upper  surface  of  the  coarse  fragments 
should  be  exposed  so  as  to  produce  a  granular  mosaic  sur- 
face for  treatment.  In  the  case  of  concrete  pavements,  the 
surface  should  be  freed  from  excess  mortar  which  by  break- 
ing up  under  impact  will  destroy  the  bond  between  the 
bituminous  material  and  the  road,  thus  promoting  disinte- 
gration. 

(c)  A  third  important  point  to  be  observed  is  that  the 
road  surface  should  be  thoroughly  dry  when  application  of 
any  hot  bituminous  material  is  to  be  made.  For  cold  sur- 
face treatments,  the  surface  may  be  very  slightly  moist, 
but  never  wet.  A  wet  surface  may  result  in  absolute  failure 
due  to  the  prevention  of  any  bond  being  produced  between 
the  road  proper  and  the  bituminous  material. 

180.  Application  of  Bituminous  Material,  (a)  Distribu- 
tion of  bituminous  materials  in  surface  treatment  is  usually 
made  by  means  of  a  tank  distributor  which  may  operate  by 
gravity  or  pressure.  Hand-pouring  pots  are  also  used  to  a 
very  limited  extent.  The  most  important  features  to  be 
observed,  in  connection  with  the  actual  application,  are  uni- 
formity of  distribution  at  the  proper  rate  per  square  yard, 
distribution  under  suitable  atmospheric  conditions,  and  in 
the  case  of  heated  materials  application  at  the  proper  tem- 
perature. All  of  these  factors  should  be  covered  by  specifi- 
cation requirements. 

(6)  Hand  pouring  should  always  be  followed  by  broom- 
ing the  material  on  the  road  surface  so  as  to  shove  ahead 
all  excess.  The  same  is  true  when  a  gravity  distributor  is 
used  except  in  case  of  treatment  with  a  very  light  dust  pre- 
ventive. Most  uniform  distribution  will  be  obtained  by  the 
use  of  a  properly  designed  and  operated  pressure  distributor. 
These  are  ordinarily  equipped  with  spraying  nozzles  so 
spaced  as  to  coat  a  considerable  width  of  surface  upon  a 
single  trip  of  the  distributor  and  so  controlled  that  multi- 


Important  Details  of  Surface  Treatment     141 

pies  of  a  given  width  may  be  treated.  The  pressure  at 
which  such  machines  operate  efficiently  is  usually  from  20 
to  75  pounds.  They  should  be  equipped  with  an  accurate 
pressure  gauge  and  a  stationary  thermometer  to  register 
the  temperature  of  heated  materials.  Rate  of  application 
is  usually  controlled  by  the  speed  of  the  distributor  and 
flow  of  material  to  the  nozzle.  Any  excess  of  material  which 
accumulates  on  the  road,  due  to  failure  to  start  the  distribu- 
tor promptly  when  the  flow  is  started,  or  failure  to  shut  off 
the  flow  promptly  when  the  distributor  stops,  should  be 
broomed  off  of  the  surface.  Clogging  of  one  or  more  nozzles 
sometimes  occurs  during  application,  causing  bare  spots  to 
appear  on  the  road  surface  after  passage  of  the  machine. 
Just  before  the  tank  is  emptied  portions  of  the  surface  may 
also  fail  to  receive  treatment.  In  such  cases  the  condition 
may  be  remedied  by  hand  pouring  and  brooming  the  bare 
spots. 

(c)  When  treatment  is  made  with  a  carpeting  medium 
it  is  important  that  the  road  surface  should  not  be  so  cold 
as  to  prevent  adhesion  of  the  bituminous  material  to  the 
surface.      To    cover   this    feature   specifications   sometimes 
provide  that  when  application  is  made  air  temperature  in 
the  shade  shall  not  be  lower  than  10°  C.   (50°  F.).     The 
proper  temperature   to  heat   a  material  intended   for  hot 
application  will  depend  upon  a  number  of  factors,  but  from 
200°  to  250°  F.  is  usually  a  safe  working  range. 

(d)  Bituminous  surface  treatments  usually  consist  of  a 
single  application  of  from  0.1  to  0.5  gallon  of  bituminous 
material  per  square  yard.     When,  however,  it  is  desired  to 
use  a  heavy  tar  or  asphalt  product  on  roads  from  which  all 
dust  and  fine  material  cannot  be  removed,   such  as  clay 
gravel    roads,    the    treatment    sometimes    consists    of   two 
applications.    The  first  application  may  then  be  made  with 
a  thin  fluid  product  applied  cold,  which  is  absorbed  by  the 
road  surface  and   serves  as  a   primer  for  a  more  viscous 
product,  which  is  next  applied  in  a  heated  state. 


142          Bituminous  Surface  Treatments 

181.  Application  of  Mineral  Cover,  (a)  When  it  is  de- 
sired to  build  up  a  bituminous  mat  or  carpet  upon  a  road 
surface,  or  when  the  character  and  rate  of  application  of 
the  bituminous  material  are  such  that  it  is  likely  to  adhere 
to  the  wheels  of  passing  vehicles  and  be  stripped  from  the 
surface,  a  thin  cover  of  fine  broken  stone,  gravel,  or  similar 
material  is  spread  upon  the  treated  surface  before  it  is 
opened  to  traffic.  In  general,  this  cover  should  be  reduced 
to  the  minimum  required  to  blot  up  the  excess  of  bitumi- 
nous material  which  has  not  been  absorbed  by  the  road 
surface.  Too  heavy  a  cover  is  frequently  applied,  in  which 
case,  after  being  ground  up  under  traffic,  the  bituminous 
mat  produced  is  overloaded  with  mineral  matter  and  soon 
crumbles  and  wears  away.  It  is  far  better  practice  to  at 
first  apply  too  little  cover  and  then  after  traffic  is  admitted 
on  the  road  to  promptly  spread  additional  mineral  matter 
where  its  need  is  indicated.  Over  one  cubic  yard  of  mineral 
matter  will  seldom  be  required  for  each  25  gallons  of  bitumi- 
nous material  applied,  and  frequently  less  may  be  used  to 
advantage,  particularly  if  the  surface  is  finished  off  by 
rolling. 

(6)  Mineral  cover  is  ordinarily  spread  from  piles  placed 
along  the  sides  of  the  road.  Small  mechanical  distributors 
have  been  designed  for  this  purpose,  but  their  use  is  usually 
limited  to  seal  coat  work  (§§  198,  267,  272)  in  bituminous 
macadam  or  bituminous  concrete  construction.  Cover 
should  be  distributed  as  uniformly  as  possible  and  when 
spread  with  shovels  a  wide  side  swing  will  be  found  most 
efficient.  In  case  of  double  application  involving  the  use 
of  a  primer,  cover  is  sometimes  used  only  after  the  second 
application  of  bituminous  material.  If  spread  over  the 
priming  material,  it  should  be  used  in  barely  sufficient 
quantity  to  prevent  the  distributor  wheels  from  picking 
up  the  surface  during  the  second  application. 

(c)  Traffic  is  usually  depended  upon  to  force  the  cover 
into  combination  with  the  bituminous  material,  but  rolling 


Materials  143 

is  highly  advantageous  in  constructing  a  bituminous  carpet 
where  as  much  as  0.5  gallon  of  bituminous  material  is 
applied  per  square  yard  of  surface. 

MATERIALS 

182.  Dust  Preventives.  Bituminous  dust  preventives 
are,  as  a  rule,  relatively  thin  fluids  which  may  be  applied 
without  preheating.  The  types  commonly  encountered  are 
crude  or  topped  (§  95)  semi-asphaltic  petroleums,  heavy 
petroleum  distillates  (§  94),  petroleum  emulsions  and  emul- 
sifying oils  (§  99)  and  crude  or  dehydrated  tars  (§  102). 
They  should  be  susceptible  to  a  light  uniform  distribution 
so  as  to  saturate  the  dust  particles  on  the  road,  but  not  pene- 
trate the  road  surface  to  any  extent.  They  need  not  neces- 
sarily possess  or  develop  cementitiousness,  as  their  function 
is  not  primarily  that  of  a  binder.  To  be  of  maximum  serv- 
ice, they  should  not  volatilize  rapidly  to  any  extent  under 
ordinary  atmospheric  conditions.  Almost  any  sufficiently 
fluid  petroleum  may  be  used  as  a  dust  preventive,  and  no 
test  requirements  other  than  maximum  viscosity  and  low 
loss  by  volatilization  are  of  importance  except  as  a  means 
of  identification.  A  maximum  specific  viscosity  (§  123) 
at  25°  C.  of  10  and  a  maximum  loss  by  volatilization  (§  129) 
at  163°  C.  of  15  per  cent  is  used  to  cover  these  requirements 
by  the  U.  S.  Bureau  of  Public  Roads.  Petroleum  emulsions 
are  sometimes  prepared  from  the  heavier  non-volatile 
petroleum  residues  for  use  as  dust  preventives.  Emulsions, 
or  emulsifying  oil  produced  as  an  alkaline  sludge  in  the 
treatment  of  petroleum  distillates,  can  be  reduced  to  any 
desired  viscosity  by  mixing  them  with  the  proper  amount 
of  water.  The  former  may  even  contain  an  appreciable 
amount  of  water  as  manufactured.  Tar  dust  preventives 
should  not  carry  over  5  or  10  per  cent  of  free  carbon  (§  lOlc) 
or  show  a  specific  viscosity  at  40°  C.,  of  over  13.  As  they 
volatilize  or  harden  more  rapidly  than  petroleum  products, 


144          Bituminous  Surface  Treatments 

they  do  not  prove  effective  as  dust  preventives  for  as  long 
a  period  after  application. 

183.  Carpeting  Mediums,  (a)  Bituminous  carpeting  me- 
diums are  usually  more  viscous  fluids  than  are  the  dust  pre- 
ventives and  may  be  applied  with  or  without  preheating 
according  to  their  viscosity  at  normal  temperature.  While 
it  would  be  desirable  that  they  possess  approximately  the 
same  consistency  as  soft  bituminous  cements,  it  is  necessary 
that  they  be  more  fluid  so  that  they  will  adhere  to  a  previ- 
ously untreated  road  surface.  They  should,  however, 
possess,  or  develop  shortly  after  application,  sufficient  cemen- 
titiousness  to  bind  together  and  hold  in  place  the  mineral 
cover.  If  they  contain  a  highly  cementitious  base  they  may 
well  carry  a  relatively  high  percentage  of  volatile  constitu- 
ents which,  after  application,  will  rapidly  evaporate  and 
leave  practically  a  bituminous  cement  in  place.  This  is 
particularly  true  of  those  products  which  are  intended  for 
cold  application.  The  carpeting  mediums  in  most  common 
use  are  heavy  crude,  topped  (§  95),  or  residual  asphaltic 
petroleums,  cut-back  asphalt  cements  (§  98),  and  fluid  resid- 
ual or  refined  tars  (§  102). 

(6)  For  cold  surface  treatment  the  petroleum  carpeting 
mediums  (§  95b)  should  preferably  show  a  specific  viscosity 
(§  123)  between  80  and  120  at  25°  C.  In  order  to  develop 
a  highly  cementitious  residue  their  loss  by  volatilization 
(§  129)  at  163°  C.  may  be  allowed  to  be  as  high  as  30  per 
cent.  The  residue  so  obtained  should,  however,  show  a 
float  test  (§  124)  at  50°  C.  of  not  less  than  90.  Because  the 
presence  of  a  very  light  flux  is  desired,  cut-back  asphalts 
may  be  required  to  show  a  loss  by  volatilization  at  163°  C. 
of  between  30  and  40  per  cent  and  to  yield  a  residue  with  a 
penetration  at  25°  C.  of  from  50  to  85.  Their  specific 
viscosity  is  usually  specified  to  be  lower  than  for  the  residual 
petroleum  products  because  through  handling  before  use 
ordinary  loss  by  volatilization  may  cause  a  material  in- 
crease in  viscosity.  For  cold  surface  treatment  the  specific 


Materials  145 

viscosity  at  40°  C.  of  tars  should  not  exceed  35  and  may  be 
as  low  as  10  or  12.  Their  percentage  of  free  carbon  (§  133) 
should  not  exceed  10  or  15  per  cent. 

(c)  Petroleum  products  for  hot  application  should  pref- 
erably show  a  float  test  at  32°  C.  of  not  less  than  60 ",  but 
their  specific  viscosity  at  100°  C.  may  be  specified  as  less- 
than  60.  Their  allowable  loss  by  volatilization  at  163°  C. 
may  be  as  high  as  15  per  cent.  Tars  for  hot  application 
should  preferably  show  a  float  test  at  32°  C.  between  60 
and  150  seconds,  and  their  percentage  of  free  carbon  should 
not  exceed  15  per  cent.  All  materials  for  hot  application 
should  be  free  from  water.  When  a  cold  primer  is  to  be 
applied  just  prior  to  a  hot  application,  such  products  as 
described  under  dust  preventives  may  be  used  for  first 
application.  It  is  customary,  however,  to  use  a  petroleum 
product  as  primer  for  petroleum  carpeting  mediums  and  a  tar 
primer  when  it  is  to  be  followed  with  a  tar  carpeting  medium. 

184.  Mineral  Cover,  (a)  For  the  construction  of 
bituminous  carpets  the  mineral  cover  should  preferably 
consist  of  clean,  hard  and  tough  broken  slag,  broken  stone 
or  gravel.  No  laboratory  test  for  quality  is  usually  required, 
but  size  or  grading  of  the  product  should  be  specified.  Typi- 
cal specifications  of  the  U.  S.  Bureau  of  Public  Roads  re- 
quire at  least  85  per  cent  of  the  product  to  pass  a  J-inch 
laboratory  screen  and  at  least  85  per  cent  to  be  retained  on 
a  J-inch  laboratory  screen.  Sometimes  a  coarse  broken 
stone  product  is  allowable,  particularly  if  the  rock  is  not" 
extremely  tough.  In  such  cases  the  U.  S.  Bureau  of  Public 
Roads'  typical  specifications  require  a  product  at  least  95 
per  cent  of  which  will  pass  a  1-inch  laboratory  screen  and 
at  least  85  per  cent  be  retained  on  a  J-inch  screen.  Some- 
times sand  or  sandy  soil  may  be  used  for  cover  if  the  carpet 
is  to  be  kept  below  \  inch  in  thickness.  The  use  of  a  clay 
or  clayey  soil  should  not  be  allowed,  as  the  carpet  when  wet 
will  then  tend  to  emulsify  under  traffic  and  produce  an 
undesirable  surface. 


146          Bituminous  Surface  Treatments 

(b)  While  the  ultimate  maximum  diameter  of  fragments 
used  for  cover  should  not  exceed  the  average  thickness  of 
carpet,  rolling  and  traffic  tend  to  rapidly  crush  the  larger 
fragments.  A  cover  of  broken  stone  of  one  inch  diameter 
cannot  be  spread  so  as  to  blot  up  the  bituminous  material 
unless  an  excess  is  used.  Rolling  is,  therefore,  particularly 
desirable  after  such  a  coarse  cover  is  used. 

185.  Field  Tests.     The  Inspector  has  but  little  to  do  in 
the  way  of  making  field  tests  when  inspecting  bituminous 
surface  treatments.     He  is  not  expected  to  test  bituminous 
materials    for    quality    although    when    purchase    is    made 
mainly  upon  a  specific  gravity  or  degree  Baume  basis  he 
may  possibly  be  required  to  make  a  test   (§  383a)   on  a 
sample  from  each  treatment.     When  the  bituminous  ma- 
terial is  to  be  applied  hot  he  should  ascertain  its  tempera- 
ture and  see  that  specification  requirements  in  this  connec- 
tion are  carried  out.     He  may  also  be  required  to  note  air 
temperatures  when  application  is  made.     Size  or  grading 
tests  of  broken-stone  or  gravel  cover  may  usually  be  made 
with  a  J-inch  and  a  J-inch  or  1-inch  field  screen,  as  may  be 
desirable. 

186.  Measurements,     (a)  The    basis    of    payment    for 
bituminous  surface  treatment  may  be  the  number  of  square 
yards  of  surface  actually  treated  or  may  include  separate 
items  for  work  and  materials  used.     The  finished  depth  of 
carpet  is  seldom  specified.    In  addition  to  measurements  of 
length  and  width,  the  Inspector  should  in  all  cases  measure 
the  quantities  of  bituminous  material  and  cover  actually 
used  if  for  no  other  reason  than  to  ascertain  their  rate  of 
application,  which  is  usually  covered  by  the  specifications. 
For  surface  treatment  bituminous  materials  are  purchased 
by  the  gallon  (§  107)  and  may  be  measured  in  original  tank 
containers  (§  365)  or  distributors.     If  measured  in  barrels 
it  will  be  advisable  to  weigh  the  contents  of  a  representative 
number  of   barrels  and   from  the   specific   gravity  of  the 
material  to  ascertain  its  gallonage  (§  1076) .    If  volume  meas- 


Materials 


147 


urement  is  made  of  a  heated  material,  a  correction  for  tem- 
perature will  be  necessary  (§  108).  Volume  or  weight  meas- 
urements (§§  35-37)  of  mineral  cover  in  cars  or  wagons 
may  also  be  necessary. 

(b)  As  a  guide  for  surface  treatment,  Fig.  21  may  prove 
useful.  This  diagram  shows  the  number  of  gallons  of  bitu- 
minous material  required  to  treat  each  100  linear  feet  of 


12  16  20  24 

WIDTH  OF  ROAD,  FEET 

Fig.  21     Quantities  of  Materials  Required  for  Bituminous 
Surface  Treatments 

road  surface  of  various  widths  and  at  different  rates  of 
application.  In  case  cover  is  used  it  also  shows  the  probable 
number  of  cubic  yards  which  will  be  required  for  100  linear 


148 


Bituminous  Surface  Treatments 


feet  of  road  according  to  the  width  of  surface  and  the  rate 
of  application  of  bituminous  material.     Fig.  22   shows  the 


4500 


2  4  6  8  10 

WIDTH  OF  APPLICATION,  FEET 


12 


Fig.  22     Length  of  Road  which  may  be  Treated  with  100 
Gallons  of  Bituminous  Material 


length  of  surface  which  should  be  covered  by  each  100  gal- 
lons of  bituminous  material  applied  at  various  rates  per 


Maintenance  149 

square  yard  for  different  widths  of  application.  This  dia- 
gram may  be  used  in  estimating  the  distance  that  a  distribu- 
tor of  known  capacity  should  travel  before  emptying  itself. 
187.  Sampling.  A  sample  of  bituminous  material  (§§  109- 
115)  should  be  submitted  to  the  laboratory,  prior  to  its 
use,  from  each  shipment  received  unless  it  has  been  sampled 
and  tested  prior  to  shipment.  Such  samples  should  be 
shipped  in  quart  tin  cans.  Size  or  grading  tests  for  mineral 
cover  should  ordinarily  be  made  by  the  Inspector.  If, 
however,  the  Laboratory  requires  samples  to  be  submitted, 
each  sample  should  weigh  approximately  10  pounds  and  be 
shipped  in  a  close-woven  cloth  bag.  When  the  size  or  grad- 
ing of  cover  is  specified,  a  sample  should  be  tested  from 
each  bulk  shipment  (§40).  If  hauled  in  wagons,  the  In- 
spector should  test  at  least  one  sample  for  every  2000  linear 
feet  of  road  treated. 


MAINTENANCE 

188.  Methods.  The  maintenance  of  a  bituminous  sur- 
face or  carpet  usually  consists  in  retreatment  with  material 
similar  to  that  originally  used.  Retreatment  may  be 
required  as  frequently  as  once  a  year,  or  several  years 
may  elapse  before  it  becomes  necessary.  The  amount 
applied  per  square  yard  is  usually  much  less  than  in  the 
original  treatment  unless  a  very  thin  carpet  was  produced, 
although  it  is  seldom  possible  to  apply  less  than  0.1  gallon 
per  square  yard  uniformly.  Sometimes  maintenance  also 
involves  repairs  to  broken  spots  in  a  mat  or  carpet.  Such 
repairs  should  be  made  by  first  cleaning  out  the  depres- 
sions, hand  pouring  the  bituminous  material,  and  spreading 
cover  at  the  broken  spots.  Retreatments  serve  not  only 
to  build  up  a  carpet  which  has  worn  away  to  a  considerable 
extent,  but  also  to  rejuvenate  it.  For  the  latter  purpose  a 
cold  application  of  relatively  fluid  bituminous  material  is 
advisable. 


150  Bituminous  Surface  Treatments 

189.  Inspection.  Inspection  of  maintenance  should  be 
similar  to  that  required  for  the  original  treatment.  When 
it  involves  repairs  to  broken  spots  in  an  old  carpet  the  great- 
est care  should  be  exercised  in  preventing  the  use  of  an 
excessive  amount  of  material  at  such  spots,  or  soft  fat  places 
in  the  surface  will  be  developed  under  traffic. 


INSPECTOR'S  EQUIPMENT 

190.  Treatment  with  Dust  Preventives.     The  following 
equipment  is  all  that  will  ordinarily  be  required: 

For  measurements : 

A  50-foot  steel  tape. 

A  pocket  rule  (§  387). 
For  sampling: 

A  supply  of  1-quart  tin  containers. 

A  supply  of  gum  labels  for  identification  information. 
For  records  and  reports : 

A  field  diary  and  pencil. 

A  supply  of  report  forms  (§  404) . 

A  carbon  paper  for  duplication  of  reports. 

191.  Treatment  with  Carpeting  Mediums.     In  addition 
to  that  listed  for  treatment  with  dust  preventives,  the  In- 
spector may  require  the  following  equipment: 

For  testing: 

A  thermometer  (§  386). 

Two  field  screens  (§371)  as  may  be  required  by  specifi- 
cations.   Openings  of  J  inch  and  J  or  1  inch  are  sug- 
2$nii>»:  gested. 

A  spring  balance  with  pan  capacity  of  10  pounds  (§  371). 
')l(fjn')f)itfiio')  JJ  01  !W}  u  qu  blind  oJ 

'    :lSto. 

' 


JtlHTe 

CHAPTER  X 

INSPECTION  OF  BITUMINOUS  MACADAM 
PAVEMENTS 

GENERAL  CHARACTERISTICS 

192.  Definition.     "A    bituminous    macadam    pavement1 
is  one  having  a  wearing  course  of  macadam  with  the  inter- 
stices   filled    by   penetration   methods   with   a   bituminous 
binder."    This  definition  represents  present  use  of  the  term 
and  classes  the  bituminous  macadam  apart  from  a  wearing 
course  constructed  by  mixing  broken  stone  with  bituminous 
material   and   from   a   macadam   which   has   been   surface 
treated  with  bituminous  material.     The  kind  of  foundation 
upon   which   the   bituminous   macadam   wearing   course   is 
laid  has  no  connection  with  the  use  of  this  term. 

193.  Usual  Method  of  Construction.    There  are  a  number 
of  methods  of  constructing  bituminous  macadam  pavements, 
but  with  occasional  minor  variations  the  method  used  in 
this  country  is  as  follows.     Upon  the  foundation  course  is 
spread  a  layer  of  broken  stone  which  is  compacted,  as  in 
plain  macadam  construction,  but  without  the  use  of  water 
or  screenings.     Upon  this  layer  of  compacted  stone  hot 
bituminous  material  is  then  applied  in  such  quantity  as 
not  merely  to  cover  the  surface  but  to  flow  into  the  voids 
between  tne  stone  fragments.     The  surface  voids  in  the 
course  are  next  filled  by  spreading  and  rolling  in,  a  thin 
layer  of  stone  chips.     After  removing  all  excess  of  loose 
chips  a  second  application  or  seal  coat  of  bituminous  mate- 
Special  Committee,   Materials  for  Road  Construction,  Am.  Soc. 

Civ.  Eng. 

151 


152  Bituminous  Macadam 

rial  is  made,  covered  with  stone  chips,  and  the  road  com- 
pleted by  rolling. 


DETAILS   OF  CONSTRUCTION 

194.  Foundations,     (a)  When  constructing  a  bituminous 
macadam    pavement   from    subgrade   up,    a   broken    stone 
foundation  is  commonly  laid  in  exactly  the  same  manner  as 
for  waterbound   macadam   (§§  165a,  166a).     When   this  is 
done  it  is  preferable  that  the  voids  in  the  foundation  should 
be  filled  with  screenings  so  as  to  prevent  the  bituminous 
material  from  draining  through  and  thus  causing  a  deficiency 
of  binder  in  the  wearing  course  which  is  later  constructed. 
Less  frequently  a  Portland  cement  concrete  foundation  is 
constructed,  but  as  heavy  motor  truck  traffic  increases  the 
use  of  a  concrete  foundation  for  the  heavily  traveled  bitu- 
minous macadam  roads  will  probably  become  much  more 
common. 

(6)  Quite  often  an  old  macadam,  slag  or  gravel  road  is 
made  to  serve  as  foundation  for  the  bituminous  macadam 
pavement.  If  the  old  surface  is  in  good  shape  it  may  be 
swept  free  of  dirt  and  excess  fine  material  and  the  bitumi- 
nous macadam  placed  directly  upon  it.  If  badly  out  of 
shape  it  should  first  be  repaired  by  patching  (§  1736)  or 
resurfacing  (§  173c). 

195.  Spreading  and  Compacting  Coarse   Stone.     When 
constructing    bituminous    macadam    the    coarse    stone    is 
spread  exactly  as  for  ordinary  macadam  (§  165a)  to  produce 
a  compacted  depth  of  between  2  and  3  inches.    Even  greater 
caution  should,  however,  be  exercised  to  see  that  no  segre- 
gation of  sizes  in  the  broken-stone  product  occurs   during 
spreading.     The  stone  should  be  rolled  dry  as  in  macadam 
construction  (§  1666)  until  the  fragments  have  interlocked. 
Rolling   should    then   cease.     The   extent   of    rolling    is  a 
most   important  matter.     If  the   stone  is  not   thoroughly 
interlocked  before  the  bituminous  material  is  applied,  it  is 


Details  of  Construction  153 

difficult,  if  not  impossible,  to  properly  consolidate  the  road 
for  heavy  traffic,  after  application  of  the  bituminous  material. 
If,  however,  the  stone  is  rolled  beyond  the  point  of  inter- 
locking, dust  begins  to  accumulate  on  the  surfaces  of  the 
fragments  and  tends  to  prevent  proper  adhesion  of  the  bitu- 
minous material.  There  is  also  danger  of  filling  the  voids 
with  fine  material  produced  by  crushing  the  larger  frag- 
ments under  the  roller  and  thus  preventing  uniform  pene- 
tration. In  the  case  of  relatively  soft  stone,  over-rolling 
should  be  particularly  guarded  agianst,  and  in  the  case  of 
relatively  hard  stone  under-rolling  should  be  especially 
avoided.  If,  after  rolling,  any  surface  irregularities  appear 
they  should  be  remedied  by  loosening  the  surface  and  re- 
moving or  adding  coarse  stone  as  may  be  required.  The 
main  object  is  to  secure  a  firm,  even  course  of  broken  stone 
uniformly  open  or  porous,  so  as  to  allow  uniform  penetra- 
tion of  the  bituminous  material  which  is  next  applied.  After 
compaction  no  traffic  should  be  allowed  to  pass  over  the 
coarse  stone  prior  to  application  of  the  bituminous  material. 

196.  First  Application  of  Bituminous  Material,  (a)  No 
bituminous  material  should  be  applied  unless  the  entire 
depth  of  coarse  stone  is  thoroughly  dry  and  the  air  tem- 
perature in  the  shade  is  50°  F.  or  mo"  re.  Before  applica- 
tion is  made  any  of  the  stone  which  has  become  mixed  or 
coated  with  dirt  should  be  removed  and  replaced  with  clean 
stone  tamped  or  rolled  into  place.  All  ruts,  bumps,  or  de- 
pressions should  be  remedied  prior  to  application. 

(6)  The  bituminous  material,  consisting  of  asphalt  cement 
or  refined  tar,  is  applied  hot  either  by  means  of  hand  pouring 
or  with  distributors.  The  proper  temperature  of  applica- 
tion for  asphalt  cements  usually  lies  between  275°  F. 
and  350°  F.,  while  for  tar  products  a  range  of  200°  F.  to 
250°  F.  is  proper.  The  material  should  be  sufficiently  fluid 
when  applied  to  penetrate  the  course  and  not  congeal  as 
soon  as  it  touches  the  road  surface,  but  great  care  should  be 
exercised  that  it  is  not  overheated  and  thereby  injured.  It 


154  Bituminous  Macadam 

is  not  advisable  to  exceed  the  maximum  temperature  limits 
above  mentioned  both  from  the  standpoint  of  injury  and 
proper  distribution.  One  of  the  most  important  details  to 
observe  is  that  of  uniform  application  at  the  proper  rate. 
From  1J  to  If  gallons  per  square  yard  is  usually  specified 
for  a  compacted  2j-inch  course  of  broken  stone.  On  the 
basis  of  30  per  cent  of  voids  about  4|  gallons  per  square 
yard  would  be  required  to  completely  fill  the  course,  but  no 
attempt  is  made  to  do  this,  as  such  quantity  would  not  only 
cause  excessive  bleeding  in  the  finished  road  but  would  make 
it  shifting  and  unstable  under  traffic.  The  main  object  is 
to  coat  the  stone  fragments  so  that  surface  contact  will  bond 
them  together.  If  when  applied  the  bituminous  material 
is  too  fluid  it  is  evident  that  the  greater  portion  will  find 
its  way  down  to  the  bottom  of  the  course,  which  is  not 
desirable. 

(c)  When  application  is  made   by  hand   pouring,  wide- 
mouthed  pouring  pots  should  be  used  which  will  distribute 
uniformly  for  a  width  of  not  less  than  8  inches.    A  pot  with 
a  J-inch  spout  will  also  be  found  useful  in  touching  up  places 
where  the  surface  may  have  been  missed  on  first  applica- 
tion.    Pouring  should  begin  at  one  edge  of  the  road  and 
proceed  uniformly  across  its  entire  width.     The  spout  of 
the  pot  should  be  held  close  to  the  road  surface.    An  excel- 
lent method  is  to  pour  diagonally  across  the  center  line  of 
the  road  so  as  to  consume  the  contents  of  a  pot  at  one  trip 
across.    The  distance  which  should  be  covered  in  uniformly 
emptying  a  pot  carrying  a  measured  quantity  of  material, 
so  as  to  secure  the  proper  rate  of  application,  should  be 
carefully  determined  and  constantly  checked  as  the  work 
proceeds.     As  an  aid  to  uniform  distribution  alternating 
the  direction  of  pouring  of  each  succeeding  pot  is  desirable. 

(d)  When  application  is  made  with  a  distributor  the  same 
general  method  is  used  and  the  same  precautions  observed 
as  for  surface  treatments  (§  1806).     Additional  precaution 
should,  however,  be  taken  to  avoid  rutting  the  compacted 


Details  of  Construction  155 

stone.  A  pressure  distributor  with  very  wide  tires  is  desir- 
able and  should  ordinarily  be  hauled  by  the  roller  during 
application.  If  a  hose  and  nozzle  distributor  is  used,  the 
nozzle  should  be  kept  close  to  the  road  and  pointing  directly 
down.  The  use  of  a  pouring  pot  will  usually  be  found  neces- 
sary in  touching  up  places  that  may  be  missed  by  the  dis- 
tributor. 

197.  Filling  Surface  Voids.     Immediately  after  the  first 
application  of  bituminous  material  is  made,  and  progressing 
with  it,  a  thin  uniform  layer  of  small  broken  stone  or  stone 
chips  should  be  spread  over  the  surface  in  such  quantity  as 
to  fill  the  surface  voids  and  just  cover  the  entire  surface. 
The  road  is  then  rolled  with  the  addition  of  more  stone  chips, 
if  necessary,  until  the  surface  is  thoroughly  bonded.    Broom- 
ing is  sometimes  required  during  rolling  and,  prior  to  the 
second  application  of  bituminous  material,  should  be  used 
to  clean  the  surface  and  remove  all  fine  material  which  is 
not  bonded  to  the  road. 

198.  Seal  Coat,     (a)  When  the  surface  is  thoroughly  clean 
and  dry  the  second  application,  or  seal  coat,  of  bituminous 
material  is  spread  usually  at  the  rate  of  from  f  to  f  gallon 
per  square  yard.    The  second  application  is  made  in  exactly 
the  same  manner  as  described  for  the  first,  by  means  of  either 
pouring  pots  or  distributor.     If  the  first  application  has 
been  made  by  hand  pouring  diagonally  across  the  road,  the 
second  application  is  made  to  cross  the  pouring  lines  of  the 
first,  and  more  than  one  trip  is  required  to  empty  the  pot. 

(6)  The  second  application  should  be  immediately  covered 
with  stone  chips  as  described  for  the  construction  of  bitumi- 
nous carpets  (§  181)  and  finished  off  by  thorough  rolling.  The 
seal  coat  and  cover  is  in  effect  a  bituminous  carpet  which 
adds  from  J  to  f  inch  to  the  finished  thickness  of  the  pave- 
ment. The  same  type  and  grade  of  bituminous  material  is 
ordinarily  used  in  both  applications,  but  sometimes  a  first 
application  of  tar  is  followed  with  a  seal  coat  of  asphalt 
cement. 


156  Bituminous  Macadam 

MATERIALS 

199.  Broken  Stone,     (a)  Rock  for  bituminous  macadam 
construction  should  possess  the  same  characteristics  as  for 
ordinary  macadam  (§167),  except  that  cementing  value  is 
an  unimportant  characteristic.    The  use  of  schist,  shale,  or 
slate  should  be  excluded  by  specifications.     The  Inspector 
should,    therefore,   be   able   to   identify   them.     A   French 
coefficient  of  wear  (§  28)  of  7  is  usually  considered  the  allow- 
able   minimum  requirement,  and    sometimes    a    minimum 
toughness  (§  29)  requirement  is  included  in  specifications. 

(6)  The  size  or  grading  of  the  coarse  broken-stone  product 
is  in  general  the  same  as  for  macadam  top  course  (§  1696) 
but  the  small  stone  or  chips  differ  from  the  screenings  used 
for  filling  and  bonding  macadam  in  that  they  should  be  as 
free  from  dust  as  possible.  Typical  specifications  of  the 
U.  S.  Bureau  of  Public  Roads  contain  the  following  require- 
ments based  upon  actual  screen  tests  which  may  be  used 
in  the  laboratory  or  in  the  field  (§371).  The  maximum 
size  of  coarse  stone  necessitates  the  construction  of  a  course 
of  not  less  than  2J  inches  compacted. 

Coarse  Stone  Per  cent 

Passing  2-inch  screen,  not  less  than,  .!T)         95 
Total  passing  1^-inch  screen  TPKVJ  .j.(Tftf{  v  25-75 
Retained  on  1-inch  screen,  not  less  than          85 

Chips: 

Passing  1-inch  screen,  not  less  than .  :.)HO-      95 
Retained  on  J-inch  screen,  not  less  than         85 

It  is  particularly  important  that  the  broken  stone  shall 
be  free  from  dirt  or  dust  occurring  as  a  coating  on  the  indi- 
vidual fragments.  . 

200.  Broken  Slag.     If  slag  (§  168)  is  used  the  require- 
ments for  quality  and  size  or  grading  are  the  same  as  for 
broken  stone.    In  addition  a  minimum  weight  per  cubic  foot 
is  also  commonly  specified,  which  property  may  have  to 


Materials  157 

be  determined  by  the  Inspector  (§375).  A  minimum 
weight  of  70  pounds  per  cubic  foot  is  sometimes  specified, 
and  a  clause  may  be  inserted  in  the  specifications  requiring 
a  certain  period  of  weathering  before  the  slag  is  used. 

201.  Asphalt  Cements.  Asphalt  cements  (§  96)  manu- 
factured to  the  desired  range  of  consistency  by  refining 
petroleum  or  by  fluxing  refined  native  asphalts  are  com- 
monly used  in  bituminous  macadam  construction.  Fluxed 
native  asphalts  containing  more  than  6  or  7  per  cent  of 
non-bituminous  material  (§§  96c,  133)  are,  however,  seldom 
employed  for  this  purpose.  The  most  desirable  consistency, 
expressed  in  terms  of  the  penetration  test  (§  125),  will  depend 
mainly  upon  climatic  conditions  to  which  the  road  is  sub- 
jected, but  may  also  be  governed  by  the  quality  of  stone 
used.  Thus  typical  specifications  of  the  U.  S.  Bureau  of 
Public  Roads  require  that  the  following  ranges  of  penetra- 
tion be  met  for  climatic  conditions  generally  prevailing  in 
the  United  States. 

Penetration 

Northern  U.  S 120-150 

Middle  Belt  U.  S 90-120 

Southern  U.  S 80-90 

These  requirements  are,  however,  very  general  and  may 
require  modification  in  particular  cases.  Thus  for  the  soft 
coralline  rock  of  Florida,  a  residual  petroleum  similar  to 
that  used  in  the  construction  of  bituminous  carpets  by  hot 
application  has  been  used  with  satisfactory  results  for  the 
climatic  and  traffic  conditions  encountered.  Under  ordinary 
conditions,  however,  the  use  of  asphah  of  over  120  penetra- 
tion creates  a  tendency  to  displacement  of  the  pavement 
under  heavy  traffic,  while  a  penetration  of  less  than  80  tends 
to  prevent  uniform  penetration  into  the  course  of  broken 
stone.  All  asphalt  cements  should,  of  course,  be  free  from 
water  and  should  not  foam  when  heated  to  the  temperature 
specified  for  application  (§  1966).  Those  which  have  not 
been  blown  usually  show  a  melting  point  by  the  ring-and- 


158  Bituminous  Macadam 

ball  method  (§  126)  of  between  35°  and  60°  G.  Their  maxi- 
mum loss  by  volatilization  at  163°  C.  (§  129)  is  seldom  over 
one  per  cent  for  oil  asphalts  and  three  per  cent  for  Bermudez 
asphalt,  which  is  the  native  asphalt  most  commonly  em- 
ployed. Penetration  of  the  residue  obtained  from  the  vola- 
tilization test  is  frequently  specified  to  be  not  less  than  one 
half  of  the  original  penetration.  Other  test  requirements 
in  specifications  are  usually  included  for  the  purpose  of 
identification  and  control  of  uniformity  (§411). 

202.  Refined  Tars.  Semisolid  refined  tars  (§  103)  are 
manufactured  to  the  desired  range  of  consistency  for  bitu- 
minous macadam  construction.  They  are  much  softer  than 
the  asphalt  cements  used  for  the  same  purpose,  and  their 
consistency  is  usually  specified  by  the  float  test  (§  124). 
Climatic  conditions  to  which  the  road  is  subjected  form 
probably  the  most  important  consideration  governing  the 
proper  float  test  limits  that  they  should  meet.  Typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads  require  the 
following  ranges  of  float  test  for  general  climatic  variations 
in  the  United  States: 

Seconds 
Float  Test 

Extreme  Northern  U.  S. ..«{{ .>m>  «!4wswKnf   90-120 
Northern  U.  S..  .^B%».THjij*>iia«cj.  fH.H®it*r>!  120-1 50 
Southern  U.  S. .  .  Jwibiafw.  *  .^In-ioW.  .)o    150-180 
These  requirements  are  of  course  very  general  and  may  be 
modified  to  meet  special  conditions.    However,  a  refined  tar 
of  less  than  90  seconds  float  test  is  apt  to  drain  to  the  bottom 
of  the  pavement  and  of  more  than  180  seconds  float  test  to 
become  very  brittle  in  cold  weather  and  to  produce  a  slip- 
pery  surface.     The   allowable   maximum   amount   of   free 
carbon  (§  102c)  which  the  tar  may  contain  is  frequently  set 
at  20  per  cent.     Refined  water  gas  tars  usually  show  less 
than  3  per  cent.     For  bituminous  macadam  construction 
where  the  thickness  of  film  of  bituminous  material  on  the 
surface  of  the  stone  fragments  is  considerably  greater  than 


Materials  159 

in  bituminous  concrete,  free  carbon  up  to  20  per  cent  may 
be  ignored  in  connection  with  the  rate  of  application  re- 
quired. No  refined  tar  for  this  class  of  work  should  contain 
water  nor  foam  when  heated  to  the  temperatures  specified 
for  application.  Upon  distillation  (§132)  the  refined  tar 
should  yield  not  more  than  1  per  cent  total  distillate  to 
170°  C.,  not  more  than  10  per  cent  to  270°  C.,  and  not  more 
than  20  per  cent  to  300°  C.  The  melting  point  by  the  ring- 
and-ball  method  (§  126)  of  the  residue  from  this  test  is  some- 
times specified  to  be  not  more  than  65°  C. 

203.  Field  Tests.     The  Inspector  is  not  usually  required 
to  make  tests  of  any  sort  upon  the  bituminous  materials 
used   in   bituminous   macadam   construction.     He   should, 
however,  keep  constant  watch  on  the  temperature  to  which 
the  product  is  heated  prior  to  application.     His  inspection 
of  the  quality  and  grading  of  broken  stone  or  broken  slag 
should  be  exactly  the  same  as  for  ordinary  macadam  con- 
struction (§  170).     As  a  guide  in  ascertaining  whether  the 
finished  road  has  been  sufficiently  compacted  a  short  stout 
screw  driver  will  be  found  useful.    If  properly  compacted  it 
should  be  difficult  to  force  this  instrument  through  the 
entire  thickness  of  pavement.     If  it  is  easily  forced  in  and 
may  be  worked  about  so  as  to  loosen  the  surrounding  stone, 
the  pavement  has  not  been  thoroughly  compacted. 

204.  Measurements,     (a)  Bituminous    macadam    pave- 
ments are  usually  measured  and  paid  for  on  the  basis  of 
square  yards  of  completed  pavement  in  place,  but  some- 
times include  separate  items  for  work  and  materials.    The 
thickness    of    completed    pavement    is    seldom    accurately 
specified,    although    a    requirement    is    frequently  included 
specifying  the  loose  or  compacted  thickness  of  coarse  stone. 
In  addition  to  the  compacted  thickness  of  coarse  stone  that 
of  the  seal  coat  or  carpet  should  be  considered  in  any  meas- 
urement of  finished  thickness.    This  will  usually  amount  to 
|  inch.     In  addition  to  measurements  of  length  and  width, 
measurements  of  loose  or  compacted  thickness  of  coarse 


160 


Bituminous  Macadam 


stone  should  be  made  by  the  Inspector.  As  a  check  upon 
this  and  also  in  connection  with  the  stone  chips,  measures 
of  quantities  by  volume  or  weight  (§§  35-37 )  of  stone  or 


16  20  24 

WIDTH  OF  ROAD,  FEET 

Fig.  23     Quantities  of  Materials  Required  for  Bituminous 

Macadam  Construction 
•.•lint*  98'TvBOO  ,.j  Hi 

slag  in  cars  or  wagons  is  advisable.  The  bituminous  ma- 
terial is  almost  always  purchased  upon  the  gallon  basis  and 
may  be  measured  in  tank,  barrel,  or  drum  containers  or  in 
kettles  or  distributors.  If  measured  in  barrels  or  drums, 


Materials  161 

it  will  be  advisable  to  weigh  the  contents  of  a  representative 
number  of  packages,  and  from  the  specific  gravity  of  the 
material  to  ascertain  its  gallonage  (§  1076).  This  will  be 
necessary  if  purchase  is  made  upon  a  weight  basis.  If 
volume  measurement  is  made  of  heated  materials,  a  correc- 
tion for  temperature  will  be  necessary  (§  108). 

(6)  As  a  guide  for  bituminous  macadam  construction  Fig. 
23  may  prove  useful.  This  diagram  shows  the  quantity  of 
coarse  stone  and  stone  chips,  loose  measure,  and  bituminous 
material  required  to  construct  each  100  linear  feet  of  pave- 
ment for  various  widths.  The  assumption  of  voids  and 
compaction  of  coarse  stone  are  as  described  for  ordinary 
macadam  (§  1716). 

The  diagram  illustrates  a  compacted  depth  of  2J  inches  of 
coarse  stone,  which  is  commonly  specified.  This  means  a 
loose  depth  of  approximately  3  inches.  A  range  of  from  1  \ 
to  If  gallons  of  bituminous  material  for  first  application  and 
from  0.4  to  0.7  gallon  for  seal  coat  is  shown,  together  with 
the  range  in  quantity  of  stone  chips  necessary  to  fill  the 
surface  voids  and  serve  as  cover  for  the  seal  coat.  This 
diagram  may  be  used  in  connection  with  the  45  per  cent  void 
curves  in  Figs.  4  and  5  in  determining  the  number  of  tons  of 
stone  used  or  required,  as  explained  under  macadam  (§  1716). 
In  the  case  of  broken  slag  where  the  weight  per  cubic  foot  or 
cubic  yard  is  usually  ascertained,  the  diagram  can  be  trans- 
lated from  volume  to  weight  basis  with  little  trouble. 

205.  Sampling,  (a)  Broken  stone  and  broken  slag  for 
bituminous  macadam  construction  should  be  sampled 
exactly  as  described  for  waterbound  macadam  (§  172). 
Samples  of  coarse  stone  to  be  tested,  usually  by  the  Inspector, 
for  size  or  grading  should  weigh  between  30  and  40  pounds 
and  samples  of  chips  should  weigh  approximately  10  pounds. 
The  Inspector  should  test  at  least  one  sample  of  each  product 
from  each  bulk  shipment  (§  40)  or,  if .  hauled  in  wagons,  at 
least  one  sample  for  every  1000  linear  feet  of  road,  and 
whenever  the  grading  of  a  product  appears  to  vary  markedly. 


162  Bituminous  Macadam 

(6)  A  sample  of  bituminous  material  (§§  109-115 )  should 
be  submitted  to  the  laboratory  prior  to  its  use  from  each 
shipment  received  unless  it  has  been  sampled  and  tested 
prior  to  shipment.  Additional  samples  should  be  taken 
whenever  there  is  any  reason  to  suppose  that  the  material 
has  been  injured  by  overheating.  Samples  should  be  shipped 
in  quart  tin  cans  with  tight-fitting  friction  tops. 

MAINTENANCE 

206.  Methods,  (a)  Ordinary  maintenance  of  a  bitumi- 
nous macadam  road  involves  surface  treatment  with  bitumi- 
nous material  and  cover,  in  which  case  both  method  and 
material  may  be  as  described  in  Chapter  IX.  Surface  treat- 
ment is  made  not  only  to  replace  or  build  up  the  original 
seal  coat  worn  away,  but  frequently  to  rejuvenate  the  bitu- 
men near  the  surface  if  it  has  hardened  materially  through 
exposure.  Cold  surface  treatments,  as  well  as  hot,  are, 
therefore,  often  made,  particularly  in  cases  where  a  tar 
seal  coat  has  ,been  used.  It  is  usually  advisable  in  such 
cases  to  use  the  same  type  of  material  as  was  employed  in 
original  construction.  In  case  an  asphalt  seal  coat  was 
originally  applied,  it  would  frequently  seem  advisable  to 
use  approximately  the  same  penetration  asphalt  as  was 
used  in  original  construction.  It  is,  however,  difficult  to 
clean  the  old  surface  so  that  the  asphalt  will  adhere  uni- 
formly to  it.  A  cut-back  asphalt  may,  however,  always 
be  used  advantageously. 

(b)  Holes,  depressions,  and  ruts  should  be  remedied  by 
cutting  them  out  so  as  to  produce  excavations  with  approxi- 
mately vertical  sides  for  the  entire  thickness  of  wearing 
course.  The  excavations  may  then  be  filled  with  coarse 
stone  which  is  compacted  and  upon  which  is  poured  bitu- 
minous material  at  the  same  rate  of  application  as  in  original 
construction.  The  patch  may  then  be  finished  as  in  original 
work.  When  making  such  patches  great  care  should  be 


Maintenance  163 

taken  not  to  use  a  surplus  of  bituminous  material,  which  will 
almost  invariably  produce  a  fat  spot  and  develop  into  a 
wave  or  bump.  The  most  convenient  method  of  patching 
is  with  a  mixture  of  broken  stone  and  emulsified  asphalt 
or  cut-back  tar  (§§  333,  334). 

(c)  When  the  pavement  is  so  badly  broken  up  or  out  of 
shape  as  to  need  resurfacing  it  should  either  be  removed  or 
scarified  and  reshaped  to  form  a  foundation  for  a  new 
pavement. 

207.  Inspection.     Inspection  of  maintenance  will  usually 
be  the  same  as  for  surface  treatment  (Chapter  IX).     For 
patching  it  will  be  similar  to  that  required  for  original  con- 
struction, in  which  case  the  extent  of  sampling  and  testing 
should  depend  upon  the  amount  of  work  and  materials 
involved. 

INSPECTOR'S  EQUIPMENT 

208.  Construction.     The  Inspector  will  find  it  advisable 
to  be  equipped  with  the  following  articles: 

For  Measurements: 
A  50-foot  steel  tape. 
A  pocket  rule  (§387). 
For  Sampling: 

A  supply  of  burlap  bags  for  sampling  stone  for  quality. 
A  ball  of  stout  twine. 

A  supply  of  eyelet  tags  for  identification  information. 
A  supply  of  1-quart  tin  cans. 
A  supply  of  gum  labels. 
For  Testing: 

A  hand  sample  of  approved  rock  for  visual  comparison 
if  broken  stone  is  used.  A  small  pocket  magnifying 
glass  may  also  prove  useful. 

A  set  of  field  screens  with  suitable  openings  as  may  be 
covered  in  specifications  for  size  (§371).  Openings 
of  2",  H",  1"  and  \"  are  suggested. 


164  Bituminous  Macadam 

A  spring  balance  with  pan  capacity  of  10  pounds  (§  371). 
A  cubic  foot  measure  for  determining  weight  per  cubic 

foot  in  case  broken  slag  is  used  (§  375). 
A  stout  screw  driver  about  6  inches  long. 
A  thermometer  (§  386)  . 
For  Records  and  Reports: 
A  field  diary  and  pencil. 
A  supply  of  report  forms  (§  404)  . 
A  carbon  paper  for  duplication  of  reports. 

209.  Maintenance.  For  maintenance  the  Inspector's 
equipment  will  ordinarily  be  the  same  as  for  surface  treat- 
ment with  carpeting  mediums  (§  191).  If  extensive  patch- 
ing is  involved,  however,  he  may  in  addition  require  certain 
items  covered  under  construction  (§  208). 


'.80S 


ioo- 


is*.)  ftit  I'f&fjp-i  lo  ^Iqqua  A 
^tQicijsI  iiiij   -la    Ii^  iA 


• 


CHAPTER  XI 

INSPECTION  OF  CONCRETE  FOUNDA- 
TIONS AND  PAVEMENTS 


GENERAL  CHARACTERISTICS' 


210.  Composition.     Without  descriptive  prefix  the  term 
" concrete"  is  generally  understood  in  this  country  to  mean 
a  mixture  of  Portland  cement  (§  65)  with  coarse  and  fine 
mineral  aggregate  and  water.     Coarse  aggregate  may  con- 
sist of  broken  stone,  broken  slag,  gravel  or  shell  which  will 
be  retained  on  a  J-inch  screen.    Fine  aggregate  may  consist 
of  sand,  or  screenings  from  any  of  the  above-mentioned  ma- 
terials which  will  pass  a  f-inch  screen.     While  Portland 
cement  is  almost  invariably  used  as  the  bonding  element 
for  concrete  road  structures,  natural  cement  (§  72)  or  Puz- 
zolan  cement  (§61)  may  be  used  to  serve  a  similar  purpose. 

211.  Proportioning.     The  strength  and  other  resistant 
qualities  of  well-mixed  and  well-cured  concrete  depend  not 
only  upon  the  quality  of  the  various  constituents  but  upon 
the  relative  proportions  in  which  they  are  present.     In 
specifications  these  proportions  are  almost  invariably  stated 
upon  a  volume  basis  for  cement,  fine  aggregate  and  coarse 
aggregate.    Thus  a  1:  2:  4  concrete  is  composed  of  one  part 
by  volume  of  cement,  two  parts  by  volume  of -fine  aggregate, 
and  four  parts  by  volume  of  coarse  aggregate.     Various 
proportions  are  used  in  highway  work,  depending  upon  the 
conditions  to  which  the  concrete  will  be  subjected,  its  thick- 
ness and  the  character  of  the  fine  and  coarse  aggregates. 
Within  certain  limits  the  strength  of  concrete  depends  upon 
the  proportion  of  cement  which  it  contains.    As  cement  is, 

165 


166     Concrete  Foundations  and  Pavements 

however,  by  far  the  most  expensive  constituent,  its  propor- 
tion is  kept  as  low  as  practicable,  particularly  in  foundation 
work.  A  lean  concrete  is  one  containing  a  relatively  small 
proportion  of  cement  such  as  1  part  to  9  parts  of  fine  and 
coarse  aggregate  combined,  while  a  rich  concrete  is  one 
containing  a  relatively  large  proportion  of  cement  such 
as  1  part  to  5  parts  of  total  aggregate.  The  exact  proportion 
of  water  to  be  used  in  mixing  concrete  cannot  be  specified 
to  advantage,  but  this  matter  is  controlled  by  describing 
the  consistency  which  the  wet  mix  should  possess  and  after 
work  has  commenced  measuring  the  amount  which  will 
produce  the  desired  consistency  and  adhering  to  such  pro- 
portion as  long  as  uniformity  in  consistency  is  maintained 
thereby. 

212.  Properties.     After  setting,  concrete  is  a  monolithic 
mass  possessing  considerable  compressive  strength  but   not 
sufficient  tensile  strength  to   prevent   the  development  of 
contraction  cracks  in  cold  weather  when  laid  under  ordinary 
conditions,  as  a  large  slab  upon  a  natural  soil  subgrade. 
Its  hardness,  toughness,  and  resistance  to  abrasion  are  largely 
dependent  upon  the  extent  to  which  these  properties  are 
possessed  by  the  coarse  aggregate  material  which  always 
predominates.     The   coarse  aggregate,   however,   is   bound 
together  with  mortar  composed  of  fine  aggregate  and  cement 
and  the  strength  of  the  entire  mass  is  greatly  influenced 
by  the  character  and  grading  of  the  aggregate  and  the  prcn 
portion  of  cement  which  it  carriest-foq 

213.  Types   of  Construction.     Considering  the  highway 
proper  there  are  two  general  types  of  concrete  construction, 
depending  upon  the  immediate  use  to  which  the  structure 
will  be  put.     These  are  foundation  and  pavement  proper. 
For  both,  the  method  of  construction  is  quite  similar.    As, 
however,  the  concrete  foundation  is   protected  from  many 
of  the  destructive  agencies  to  which  the  pavement  is  sub- 
jected,  the   proportion  and  even  the  character  of  its  con- 
stituents may  be  quite  different.     The  concrete  pavement, 


Important  Details  of  Construction        167 

like  the  foundation,  is  usually  laid  in  a  single  course  upon 
the  prepared  subgrade,  but  sometimes,  to  lower  cost  and 
utilize  local  material,  which  is  not  suitable  for  wearing 
surface,  the  pavement  is  laid  in  two  courses.  In  such  cases 
the  lower  course  maybe  considered  as  foundation,  although 
before  it  sets  the  upper  course  is  laid  upon  it  so  as  to  produce 
a  single  monolithic  structure  throughout  the  entire  depth. 
Foundations,  as  such,  are  seldom  laid  with  expansion  joints 
but  quite  frequently  transverse  expansion  joints  are  con- 
structed throughout  the  entire  depth  of  concrete  pavements 
at  regular  intervals.  Such  joints  are  usually  filled  with 
bituminous  material  or  a  prepared  bituminous  expansion 
joint  (§§  328-330).  Occasionally  the  concrete  pavement  is 
reinforced  with  metal  (§  342)  embedded  in  the  concrete 
during  construction.  Frequently  the  design  of  concrete 
foundation  or  pavement  includes  an  integral  curb  construc- 
tion. In  the  case  of  foundation  work  this  may  also  involve 
the  construction  of  a  concrete  gutter  simultaneously  with 
that  of  the  foundation  and  curb. 

IMPORTANT  DETAILS  OF  CONSTRUCTION 

214.  Preparation  of  Subgrade.     Subgrade  preparation  for 
concrete  foundations  and  pavements  is  quite  similar  to  that 
described  for  macadam  construction  (§  164).    The  subgrade 
is  usually  made  flat  or  without  crown.     Sometimes,  how- 
ever, as  in  the   case   of  alley  construction,  if  the   surface 
carries  a  dished  or  inverted  crown,  that  of  the  subgrade  is 
made  to  conform  with  it.     With  this  exception,  therefore, 
the  thickness  of  a  concrete  foundation  or  pavement  is  not 
uniform  throughout  its  width,  but  is  greater  at  the  center 
than  at  the  sides. 

215.  Proportions,     (a)  The  relative  proportion  (§211)  of 
constituents  to  be  used  in  the  preparation  of  concrete  may 
be  specified  upon  a  very  definite  volume  basis  such  as  1:3:6 
or  1:  li:  3.    When  mixing,  however,  it  may  be  found  desir- 


168    Concrete  Foundations  and  Pavements 

able  to  slightly  vary  the  relative  amounts  of  fine  and  coarse 
aggregate  so  as  to  obtain  a  denser  mix  or  one  which  can  be 
worked  more  readily.  It  is,  therefore,  preferable  that  speci- 
fications state  definitely  the  proportion  of  cement  to  total 
coarse  and  fine  aggregate  such  as  1 :  9  and  to  further  require 
that  it  shall  approximate  a  more  definite  composition  such 
as  1 :  3 :  6.  In  addition  specifications  may  definitely  require 
a  stated  amount  of  cement  to  be  used  per  cubic  yard  of 
concrete. 

(6)  Selection  of  the  most  economical  and  desirable  pro- 
portions for  any  given  work  will  depend  upon  a  number  of 
considerations.  In  general  it  is  desired  to  obtain  a  concrete 
of  maximum  density.  The  percentage  of  voids  in  both 
coarse  and  fine  aggregate  is,  therefore,  an  important  factor. 
In  order  to  fill  voids  under  practical  working  conditions, 
however,  it  is  necessary  to  use  somewhat  more  than  the 
theoretical  amounts  of  void- filling  material.  For  founda- 
tion construction  proportions  of  cement  to  total  aggregate 
usually  lie  between  1 :  10J  and  1 :  6.  Common  specific  pro- 
portions are  1:3:6  and  1:2J:5.  For  concrete  pavements, 
proportions  of  cement  to  total  aggregate  lie  between  1 :  6 
and  1:4.  Best  practice  seems  to  call  for  specific  proportions 
of  1:2:3  for  broken-stone  concrete  and  1:  1J:3  for  gravel 
concrete.  In  two-course  work,  the  proportions  may  differ 
for  the  individual  courses.  Thus,  the  Committee  on  Con- 
crete Roads  and  Pavements  of  the  American  Concrete 
Institute  has  recommended  for  bottom  course  a  1 :  2J : 4 
mix  and  for  top  course  a  1 :  If :  2|  mix. 

(c)  Products  which  consist  of  a  combination  of  coarse  and 
fine  aggregates  should  not  be  used  in  concrete  mixtures 
unless  first  screened  and  recombined  in  proper  proportions. 
This  is  due  to  the  fact  that  such  products  are  seldom  uni- 
form, and  unavoidable  segregation  of  sizes  will  result  dur- 
ing handling.  In  some  specifications,  however,  as  much  as 
15  per  cent  of  fine  aggregate  passing  the  ^-inch  screen  is 
allowed  to  be  present  in  the  coarse  aggregate  (§  222,6 ,c) 


Important  Details  of  Construction        169 

and  as  much  as  15  per  cent  of  coarse  aggregate  retained  on 
the  J-inch  screen  is  allowed  to  be  present  in  the  fine  aggre- 
gate (§  2236).  This  is  only  permissible  when  due  allowance 
is  made  in  setting  the  proportions  actually  measured,  and 
when  specifications  are  based  upon  a  fixed  proportion  of 
cement  to  combined  coarse  and  fine  aggregate.  It  may  be 
assumed  that  the  presence  of  15  per  cent  or  less  of  fine 
aggregate  in  the  coarse  only  exists  as  a  void-filling  medium 
and  that  a  measured  volume  of  the  coarse  aggregate  would 
not  be  noticeably  reduced  by  the  removal  of  this  fine.  It 
may  also  be  assumed  that  the  removal  of  15  per  cent  or  less 
of  coarse  aggregate  from  the  fine  will  not  reduce  its  volume 
15  per  cent  because  the  large  particles  exist  as  individuals 
suspended  in  the  mass  of  fine  aggregate.  The  removal  of 
any  number  of  particles,  therefore,  reduces  the  volume  of 
fine  aggregate  only  by  the  absolute  volume  of  such  particles 
and  the  percentage  of  voids  in  the  remaining  fine  aggregate 
is  greater  than  it  was  before.  With  these  considerations 
in  mind  and  working  on  a  45  per  cent  void  basis  for  both 
coarse  and  fine  screened  aggregates,  the  following  formulas 
may  be  used  to  ascertain  the  actual  number  of  parts  of 
coarse  and  fine  aggregate  which  should  be  measured  in  order  to 
conform  with  any  specified  proportions.  In  these  formulas, 

a  =  per  cent  of  coarse  aggregate  passing  the  J-inch  screen. 
6  =  per  cent  of  fine  aggregate  retained  on  the  J-inch  screen. 
p  =  parts  by  volume  of  coarse  aggregate  required  to  1  part 

of  cement. 
p'  =  parts  by  volume  of  fine  aggregat"  required  to  1  part 

of  cement. 

x  =  parts  by  volume  of  coarse  aggregate  to  actually  use. 
y  =  parts  by  volume  of  fine  aggregate  to  actually  use. 

5(2000p  -  2Qbp'  -  llbp) 
10000  -  556  -  ab 

100(1002^02)  _ 
y  "  10000  -  556  -  ab. 


170     Concrete  Foundations  and  Pavements 

If  in  these  formulas  a  and  b  are  both  zero,  then  x  =  p 
and  y  =  p'.  To  illustrate  the  use  of  these  formulas,  suppose 
a  1:2:4  mix  is  required  from  coarse  aggregate  containing 
15  per  cent  fine  particles,  and  fine  aggregate  containing  15 
per  cent  coarse  particles.  Then 

_  5[(2000  x  4)  -  (20  x  15  x  2)  -  (11  x  15  x  4)] 

10000-  (55  x"l5)  -  (15  x  15) 
33700 


8950 


3.77 


100[(100  x  2)  -  (15  x  4)]  _  14000  _ 
8950  =  8950  = 

The  actual  proportions  to  measure  would  then  be  1:  1.6:  3.8 
instead  of  1:  2:4.  While  the  proportion  of  cement  to  total 
fine  and  coarse  aggregate  is  apparently  greater  than  that 
required,  it  is  not  in  reality,  as  may  be  demonstrated  by 
separating  both  aggregates  on  the  J-inch  screen  and  measur- 
ing them  separately. 

216.  Mixing.  Concrete  for  foundation  and  pavement 
construction  is  almost  invariably  mixed  by  machines  of 
which  there  are  two  general  types,  the  batch  mixer  and 
the  continuous  mixer.  The  use  of  a  batch  mixer  is  com- 
monly specified  because  control  of  uniformity  of  output  is 
more  assured.  With  a  batch  mixer  of  known  capacity  the 
proper  amounts  of  coarse  aggregate,  fine  aggregate  and 
cement,  to  give  the  specified  proportions,  are  measured  and 
introduced  into  the  mixing  drum.  A  measured  quantity  of 
water  is  then  added,  after  which  mixing  should  be  carried 
on,  preferably  for  a  full  minute.  This  is  an  important  matter 
which  should  be  covered  by  specifications.  Some  mixers 
are  equipped  with  timing  devices  to  insure  that  each  batch 
gets  the  proper  amount  of  mixing,  also  with  water  measur- 
ing and  discharging  devices,  the  use  of  which  is  very  desir- 
able. After  mixing  a  batch,  the  entire  contents  of  the 
mixer  should  be  discharged  before  attempting  to  mix  a 
new  batch. 


Important  Details  of  Construction        171 

217.  Consistency.     The  consistency  of  fresh  concrete,  is 
controlled  by  the  amount  of  water  used  and  should  be  such 
as  to  flatten  out  and  quake,  when  deposited,  but  not  flow 
or  segregate.    The  proper  quantity  of  water  should  be  deter- 
mined by  the  Engineer  and  not  varied  without  his  consent. 
As  a  rule,  in  order  to  obtain  maximum  strength  as  little  water 
should  be  used  as  possible  to  secure  a  product  which  may 
be  properly  placed  and  finished.    Because  of  increased  ease 
in  working  a  strong  tendency  exists  to  use  more  water  in 
the  mix  than  is  desirable. 

218.  Placing  and  Shaping,     (a)  The  concrete  should  be 
placed  between  suitable  side  forms  held  rigidly  in  position. 
If  inside  stakes  are  used  they  should  be  removed  as  they 
are  reached  in  placing  the  concrete.    The  forms  should  have 
the  same  height  as  the  specified  thickness  of  concrete  at 
the  sides  and  should  be  well  greased  or  soaped  prior  to 
placing  the  concrete.    At  time  of  placing  concrete  the  sub- 
grade  should  be  neither  bone  dry  nor  wet.    If  dry  or  dusty 
it  should  be  lightly  sprinkled  with  water.    Concrete  is  some- 
times  deposited  from  the  mixer  by  means   of  boom  and 
bucket  and  sometimes  by  open  chute.     In  either  case  care 
should  be  taken  that  segregation  of  the  aggregate  does  not 
occur.     If  a  chute  is  used  its  pitch  should  be  sufficient  to 
deliver  concrete  of  the  proper  consistency.    Concrete  should 
be  spread  to  the  required  depth  by  means  of  shovels  and 
not  with  rakes,  and  it  should  be  well  spaded  against  forms. 
Strike  boards  and  lutes  may  also  be  used  to  place  concrete. 
Concrete  should  not  be  placed  upon  a  frozen  subgrade  nor 
when  the  air  temperature  is  below  3C°  F.  unless  adequate 
means  are  employed  to  heat  the  aggregate  and  mixing  water. 
Concrete  should  be  placed  as  soon  after  mixing  as  practic- 
able and  never  later  than  30  minutes  thereafter.    At  the  end 
of  each  working  period  a  vertical  bulkhead  should  be  placed 
across,  and  at  right  angles  to,  the  center  line  of  the  road, 
and  the  concrete  worked  up  to  and  against  it  to  produce  the 
same  cross  sectional  area  as  the  rest  of  the  work.     Upon 


172     Concrete  Foundations  and  Pavements 

removing  the  bulkhead,  the  joint  should  be  wetted  just 
prior  to  placing  new  concrete  against  it. 

(6)  If  expansion  or  contraction  joints  are  to  be  con- 
structed at  regular  intervals,  all  work  between  joints  should 
be  continuous.  Expansion  joints  should  be  constructed  by 
means  of  a  bulkhead  of  suitable  thickness  cut  to  the  exact 
cross  section  of  the  pavement.  Prepared  fillers  are  lightly 
attached  to  the  top  of  the  bulkhead  until  the  concrete  is 
placed  against  both  sides  of  it,  after  which  the  bulkhead  is 
carefully  removed  leaving  the  filler  in  place  and  the  con- 
crete on  both  sides  tamped  and  shaped  against  it.  The 
filler  should  project  above  the  finished  surface  and  later 
may  be  cut  down.  For  poured  joints  the  bulkhead  is  allowed 
to  remain  until  the  concrete  is  sufficiently  set  to  preserve 
its  edge.  It  is  then  removed  and  the  slot  later  filled  by  pour- 
ing in  the  heated  bituminous  filler.  It  is  important  that 
expansion  joints  extend  to  the  extreme  edges  and  that  they 
contain  a  suitable  filler  for  their  entire  length.  If  even  a 
half  inch  or  so  is  left  solid  at  the  end  of  the  joint,  or  becomes 
filled  with  incompressible  material,  the  corner  of  the  slab 
may  crack,  or  shear  off,  for  some  distance  back,  when  the 
concrete  expands.  If  joints  are  constructed  to  provide  for 
contraction  only,  a  thin  sheet  of  metal,  bituminous  fabric 
or  tar  paper  is  used  for  breaking  joints  and  the  work  may 
proceed  continuously.  All  expansion  joints  should  extend 
through  the  entire  thickness  of  pavement.  Contraction 
joints  are  sometimes  made  to  extend  from  the  bottom 
to  within  an  inch  or  less  of  the  finished  surface,  in  which 
case  they  are  called  invisible  joints. 

(c)  When  wire  mesh  or  expanded  metal  is  used  for 
reinforcement  it  is  usually  placed  at  least  two  inches 
below  the  surface  and  in  lapped  widths,  as  may  be 
specified,  parallel  to  or  across  the  center  line  of  the  road. 
Circumferential  reinforcing  consists  in  placing  steel  bars 
around  each  slab  near  the  edges.  When  placing  concrete 
great  care  should  be  taken  to  work  the  concrete  around 


Important  Details  of  Construction        173 

and  in  close  contact  with  all  surfaces  of  the  reinforcing 
metal. 

(d)  When  combination  foundation  or  pavement  with 
integral  curb  and  gutter,  or  curb,  is  to  be  constructed,  the 
integral  construction  should  be  placed  immediately,  and 
never  later  than  thirty  minutes,  after  the  foundation  or 
pavement  is  placed.  Such  construction  should  be  thor- 
oughly tamped  and  spaded  against  the  forms  which  have 
been  placed  for  it. 

219.  Finishing  the  Surface,  (a)  The  surface  of  concrete 
foundations  is  usually  finished  with  a  template,  cut  to  the 
desired  crown,  and  worked  from  the  side  forms.  The  sur- 
face should  be  thoroughly  compacted  and  brought  to  true 
shape  immediately  after  placing.  A  perfectly  smooth  sur- 
face is  desirable  for  the  later  construction  of  a  brick  or 
block  pavement.  For  bituminous  pavements  it  should  be 
slightly  rough,  with  the  coarse  aggregate  thoroughly  em- 
bedded but  not  covered  with  a  coating  of  mortar.  The 
finished  surface  should  be  free  from  all  depressions  or  other 
irregularities. 

(b)  There  are  various  methods  of  finishing  the  surface  oi 
concrete  pavements.  A  heavy  steel  template  is  commonly 
used  on  pavements  which  are  not  too  wide  for  compacting 
and  shaping  by  this  method.  For  very  wide  pavements 
lutes  may  be  used  for  shaping,  provided  metal  stakes  are 
set  at  intervals  across  the  road  to  serve  as  guides,  and 
pulled  out  as  soon  as  the  concrete  is  worked  around  them 
to  the  proper  height.  In  either  case  unless  a  finishing 
machine  is  used  the  concrete  should  next  be  rolled  by  hand 
with  a  long-handled  metal  roller.  This  roller  should  be 
operated  from  the  sides  of  the  road  so  as  to  pass  across  it 
from  one  edge  to  the  other,  advancing  in  a  slightly  diagonal 
direction.  The  concrete  should  be  rolled  until  free  water 
ceases  to  corne  to  the  surface.  A  final  finish  is  then  given 
with  a  strip  of  canvas  or  rubber  belting  from  6  inches  to 
1  foot  in  width  and  about  2  feet  longer  than  the  width  of 


174     Concrete  Foundations  and  Pavements 

the  road.  The  belt  should  be  worked  with  a  longitudinal 
and  crosswise  motion  in  the  same  manner  as  a  template.  A 
second  finishing  with  the  belt  should  be  given  when  the 
excess  surface  water  has  disappeared.  All  concrete  adjacent 
to  transverse  expansion  joints  should  be  finished  with  a 
split  wood  float  operated  from  a  bridge  which  should  not 
touch  the  concrete  at  any  point.  Edges  of  joints  are  rounded 
with  an  edging  tool  to  a  radius  of  approximately  ^  inch 
and  the  edges  next  to  the  side  forms  are  rounded  to  a  radius 
of  approximately  1  inch. 

220.  Curing.     As  soon  as  the  concrete  has  received  its 
final  finish,  it  should  be  protected  with  a  canvas  cover  sus- 
pended above  its  surface.    When  it  has  hardened  sufficiently 
the  canvas  protection  is  replaced  by  a  covering  of  earth  one 
inch  or  more  in  thickness.     The  earth  covering  should  be 
sprinkled  from  time  to  time  to  keep  it  moist  so  that  harden- 
ing of  the  concrete  will  proceed  slowly.     After  a  period  of 
not  less  than  10  days,  the  covering  is  removed  but  the 
pavement  kept  closed  to  traffic  for  an  additional  period  of 
from  4  to  10  days,  or  longer  if  the  air  temperature  is  below 
50°  F.     Sometimes  instead  of  using  an  earth  covering,  the 
surface  of  the  concrete  is  flooded  with  about  2  inches  of 
water  which  is  held  by  earth  dams  built  at  the  sides  and  at 
intervals  across  the  road  after  the  pavement  has  sufficiently 
hardened  under  the  canvas  protection. 

MATERIALS 

221.  Cement.     The  physical   and    chemical   characteris- 
tics of  Portland  cement  have  been  so  well  standardized 
(§  64)  that  specifications  for  its  use  in  highway  work  usually 
require  only  that  "it  shall  conform  to  the  standard  specifi- 
cations  of  the   American  Society  for   Testing   Materials," 
which  have  already  been  stated. 

222.  Coarse   Aggregate,     (a)  For   highway   construction 
broken  stone  or  gravel  is  most  commonly  used  as  coarse 


Materials  175 

aggregate,  although  broken  slag  has  also  been  used  to  some 
extent.  As  it  is  most  important  that  the  properties  of 
coarse  and  fine  aggregates  should  be  carefully  controlled, 
specifications  usually  allow  for  the  presence  of  little  or  no 
fine  material  passing  the  J-inch  screen.  Unscreened,  crusher 
or  shovel  run  products  or  unscreened  gravel  should  never 
be  used  for  coarse  aggregate.  The  material  of  which  the 
coarse  aggregate  consists  should  be  sound  and  free  from  dirt 
or  coating  of  any  sort.  Particular  attention  should  be  paid- 
to  preventing  its  admixture  with  dirt  when  stored  in  piles 
along  the  road.  The  absence  of  soft,  thin,  elongated  or 
laminated  fragments  should  be  specified. 

(6)  Laboratory  test  requirements  for  quality  of  rock  or 
gravel  used  as  coarse  aggregate  in  concrete  foundations  are 
seldom  included  in  specifications.  In  the  case  of  slag, 
however,  a  minimum  weight  per  cubic  foot  for  the  commer- 
cial product  may  be  specified,  and  60  pounds  is  not  con- 
sidered an  unreasonable  minimum  limit.  A  certain  period 
of  weathering  before  the  slag  is  used  is  also  sometimes  re- 
quired. Size  or  grading  requirements  should  preferably  be 
specified  upon  the  basis  of  laboratory  screen  tests.  As  an, 
illustration  the  following  requirements  are  cited  from  typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads  in  con- 
nection with  broken  stone  or  gravel  coarse  aggregate. 

Per  cent 

Passing  3-inch  screen,  not  less  than 95 

Total  passing  1  J-inch  screen .  .  .  . 40-75 

Retained  on  f -inch  screen,  not  less  '  han ...         85 

The  15  per  cent  of  coarse  aggregate  which  is  allowed  to 
pass  the  J-inch  screen  is,  however,  only  permissible  when 
specifications  are  based  upon  a  fixed  proportion  of  cement 
to  combined  coarse  and  fine  aggregate  and  allowance  is 
made  for  slight  variations  in  the  relative  amounts  of  coarse 
and  fine  aggregates  (§215c). 

(c)  For  the  construction  of  a  concrete  pavement  or  wear- 


176     Concrete  Foundations  and  Pavements 

ing  course,  quality  requirements  based  upon  laboratory 
tests  should  preferably  be  given  in  specifications.  Only 
tough  and  fairly  hard  material  should  be  allowed.  While 
gravel  has  been  used  to  a  considerable  extent  it  is  not  in 
general  considered  as  satisfactory  as  broken  stone,  as  its 
uniformity  of  quality  is  more  difficult  to  control.  This 
fact  is  also  true  of  broken  slag.  The  U.  S.  Bureau  of  Public 
Roads'  typical  specifications  for  broken  stone  to  be  used 
•as  coarse  aggregate  in  concrete  pavements  requires  a  French 
coefficient  of  wear  (§  28)  of  not  less  than  8  and  a  toughness 
(§  29)  of  not  less  than  8.  The  size  or  grading  of  aggregate 

is  specified  as  follows: 

Per  cent 

Passing  2-inch  screen,  not  less  than 95 

Total  passing  1-inch  screen 40-75 

Retained  on  J-inch  screen,  not  less  than .....    85 

As  in  the  case  of  foundation  material  specifications,  the 
15  per  cent  allowed  to  pass  the  i-inch  screen  is  only  per- 
missible when  specifications  are  based  upon  a  fixed  propor- 
tion of  cement  to  combined  coarse  and  fine  aggregates  and 
allowance  is  made  for  slight  variations  in  the  relative  amounts 
of  coarse  and  fine  aggregates.  If  specifications  allow  for 
the  use  of  gravel  the  soundness  of  individual  pebbles  (§  374) 
should  be  carefully  covered.  If  slag  is  allowed  a  minimum 
weight  p.er  cubic  foot  should  be  specified  in  connection 
with  a  minimum  French  coefficient  of  wear  the  same  as  for 
rock.  A  minimum  weight  per  cubic  foot  of  70  pounds  is 
sometimes  set.  A  clause  may  also  be  inserted  requiring  a 
certain  period  of  weathering  before  the  slag  is  used. 

223.  Fine  Aggregate,  (a)  The  -use  of  sand  is  most 
commonly  specified  as  fine  aggregate  for  concrete,  but  some- 
times stone  screenings  or  a  mixture  of  sand  and  stone 
screenings  is  permitted.  In  any  case  the  fine  aggregate 
should  consist  of  clean,  hard,  durable  uncoated  particles 
free  from  clay,  loam,  mica  and  organic  matter.  All  of  the 
material  is  usually  specified  to  pass  a  J-inch  screen  and  an 


Materials  177 

excess  of  silt  or  dust  is  eliminated  by  a  maximum  allowance 
for  material  which  will  pass  a  100-mesh  sieve.  In  addition 
to  grading  requirements,  specifications  frequently  include 
a  minimum  mortar  strength  test  requirement  (§  58).  Some- 
times the  use  of  a  product  which  will  not  pass  the  mortar 
strength  test  is  allowed,  provided  an  additional  amount 
of  cement  is  used  in  the  concrete  equivalent  to  the  addi- 
tional quantity  required  to  bring  the  mortar  strength  up 
to  that  specified. 

(6)  As  an  illustration  of  specification  requirements  for 
grading  and  strength  of  sand  for  concrete  foundations,  the 
following  is  taken  from  typical  specifications  of  the  U.  S. 
Bureau  of  Public  Roads: 

Per  cent 

Passing  |-inch  screen ', 100 

Total  passing  20-mesh  sieve,  not  less  than 20 

"       50     "        "        "    more  than......       50 

Passing  100-mesh  sieve,  not  more  than 10 

Removed  by  elutriation  (§  53),  not  more  than. ...         5 
Mortar  strength  of  1 : 3  briquettes,  not  less  than 
75  per  cent  of  standard  1 : 3  briquettes  made 
with  the  same  cement. 

If  stone  screenings  or  a  combination  of  screenings  and  sand 
are  allowed  to  be  used,  100  per  cent  should  be  required  to 
pass  a  J-inch  screen  and,at  least  85  per  cent  to  pass  a  J-inch 
screen.  The  15  per  cent  allowed  to  be  retained  on  the 
1-inch  screen  is  only  permissible  under  the  conditions  men- 
tioned for  coarse  aggregate  gradings  in  connection  with 
material  passing  this  screen  (§  2226) .  That  portion  of  the 
stone  screenings  which  passes  the  i-inch  screen  should  then 
be  subjected  to  the  same  grading  and  strength  requirements 
as  given  for  sand.  Sometimes  these  requirements  are  made 
as  rigid  as  for.  sand  to  be  used  in  pavement  or  wearing  course 
construction. 

(c)  Grading  and  strength  requirements  for  sand  for 
concrete  pavement  or  wearing  course  are  covered  as 


178     Concrete  Foundations  and  Pavements 

follows  by  typical  specifiactions  of  the  U.   S.   Bureau   of 

Public  Roads: 

Per  cent 

Passing  J-inch  screen 100 

Total  passing  20-mesh  sieve 50-80 

Total  passing  50-mesh  sieve,  not  more  than 20 

Passing  100-mesh  sieve,  not  more  than 5 

Removed  by  elutriation  (§  53),  not  more  than.  .  .  3 
Mortar  strength  of  1 : 3  briquettes,  not  less  than 

100  per  cent  of  standard  1 :  3  briquettes  made 

with  the  same  cement. 

224.  Water.     All  water  used  in  mixing  concrete  should 
be   reasonably   clear,   free   from   harmful   amounts   of   oil, 
acid,   alkali  or  vegetable  substance  and   neither  brackish 
nor  salty. 

225.  Reinforcing  Metal.    When  construction  involves  the 
use  of  wire  mesh  or  expanded  metal  reinforcement  a  mini- 
mum weight  of  25  pounds  per  100  square  feet  is  usually 
specified.     The  ratio  of  effective  areas  'of  the  reinforcing 
members  at  right  angles  to  each  is  also  sometimes  specified. 
If  steel  bars  are  used,  their  size  and  shape  are  specified  to- 
gether with  quality  requirements  which  can  only  be  deter- 
mined by  laboratory  test,  although  a  cold  bend  test  (§  3426) 
may  sometimes  be  made  in  the  field. 

226.  Hydrated  Lime.    When  ttys  use  of  hydrated  lime 
is  specified  in  concrete  construction,  the  lime  is  ordinarily 
required  to  meet  the  specifications  adopted  by  the  American 
Society  for  Testing  Materials  (Standard    C6-25).      These 
specifications  cover  chemical  properties  as  determined  by 
laboratory  test,   also   a  laboratory  test  for   constancy  of 
volume.    In  addition  it  is  required  that  not  more  than  \  per 
cent  shall  be  retained  on  a  30-mesh  sieve.     Hydrated  lime 
is  incorporated  in  the  concrete  on  the  basis  of  a  specified 
percentage  of  the  weight  of  cement  used.     Thus  if  10  per 
cent  of  the  weight  of  cement  is  specified  9.4  pounds  will 
be  required  for  each  bag  of  cement  used. 


Materials  179 

227.  Materials  for  Expansion  Joints.     Bituminous  fillers 
(§§  97,  104)  are  usually  specified  for  filling  expansion  joints. 
The  application  and  properties  of  such  fillers  are  described 
later  (§§328-330). 

228.  Field   Tests,     (a)  Cement,    joint-filling    materials, 
metal  reinforcing,  and  hydrated  lime  if  it  is  used,  are  usually 
subjected  to  laboratory  tests  only.     Water  for  mixing  is 
seldom  tested  unless  reason  exists  for  believing  it  to  be 
unsuited  for  use,  in  which  case  the  sample  is  submitted 
to  the  laboratory  for  examination.     Both  coarse  and  fine 
aggregates  should,  however,  be  subjected  to  field  tests  by 
the  Inspector  in  order  to  insure  proper  control  of  the  mix. 
In  addition,  if  expansion  joints  are  to  be  filled  with  heated 
bituminous  material  the  Inspector  should  observe  the  tem- 
perature to  which  it  is  raised. 

(6)  Broken  stone  for  coarse  aggregate  is  usually  approved 
upon  laboratory  tests  for  quality  made  in  advance  of  the 
work,  in  which  case  the  Inspector  will  find  it  convenient  to 
secure  a  small  specimen  from  the  sample  tested  for  the  pur- 
pose of  visual  comparison  with  the  product  furnished  on 
the  job.  If  gravel  is  used  it  should  be  examined  for  quality 
as  described  under  Gravel  Roads  (§  1516)  and  particular 
attention  paid  to  the  possible  presence  of  a  clay  coating 
on  the  individual  pebbles.  In  the  case  of  slag,  determina- 
tions of  weight  per  cubic  foot  should  be  made  from  time  to 
time.  All  products  should  be  constantly  watched  to  see 
that  they  do  not  contain  an  excess  of  thin  or  elongated 
pieces,  disintegrated  fragments,  dirt  or  other  objectionable 
material.  The  size  or  grading  of  coarse  aggregate  should 
be  frequently  determined  for  conformity  with  specification 
requirements  and  a  set  of  selected  field  screens  (§371) 
from  the  maximum  diameter  to  f  inch  should  be  used  for 
this  purpose. 

(c)  Fine  aggregate  should  be  subjected  to  visual  inspec- 
tion for  the  purpose  of  detecting  clay  or  organic  coatings 
on  the  individual  particles.  If  the  presence  of  organic 


180     Concrete  Foundations  and  Pavements 

matter  is  suspected  the  aggregate  may  be  subjected  to  a 
rough  field  test  (§  372)  to  determine  whether  there  is  suffi- 
cient present  to  make  the  use  of  the  product  inadvisable. 
Field  tests  for  the  determination  of  silt  (§  373)  may  also 
be  occasionally  required.  In  addition,  the  size  or  grading 
of  fine  aggregate  should  be  determined  at  frequent  intervals 
for  conformity  with  specification  requirements.  A  set  of 
selected  field  sieves  (§371)  in  addition  to  the  J-inch  screen 
should  be  used  for  this  purpose. 

229.  Measurements,  (a)  As  the  proportioning  of  con- 
crete is  almost  invariably  specified  upon  a  volume  basis,  it 
is  necessary  for  the  Inspector  to  keep  constant  watch  upon 
the  relative  volumes  of  the  constituents  used  for  each  batch 
in  order  to  assure  a  uniform  product.  Cement  is  commonly 
used  by  the  sack  of  94  pounds,  which  is  specified  as  one  cubic 
foot.  Coarse  and  fine  aggregates  are  measured  separately, 
usually  in  wheelbarrows  of  2  or  3  cubic  feet  capacity.  The 
contractor  should  furnish  a  1 -cubic-foot  measuring  box 
which  should  be  used  in  connection  with  each  product  for 
gauging  and  marking  the  capacity  of  wheelbarrows.  When 
the  proportions  or  size  of  the  batch  are  such  as  to  require 
fractional  capacity  loads,  such  amounts  should  be  gauged 
and  shown  by  a  line  painted  at  proper  height  around  the 
inside  of  the  barrow.  In  measuring  whole  or  fractional 
barrow  loads  the  material  should  be  struck  level  and  level 
loads  only  should  be  delivered  to  the  mixer.  In  addition 
to  capacity  measurements  the  Inspector  should  see  that 
the  proper  number  of  loads  and  fractions  of  loads  of  each 
aggregate  are  delivered  to  the  mixer  for  each  batch.  The 
same  is  true  in  connection  with  the  number  of  bags  of 
cement. 

(b)  Concrete  foundations  and  pavements  are  commonly 
paid  for  upon  a  square  yard  basis,  complete  in  place,  and 
sometimes  by  the  number  of  cubic  yards  as  determined  by 
end  area  section  and  length.  Extra  thickness  at  weak  spots 
in  the  subgrade  when  called  for  are  paid  upon  the  number 


Materials 


181 


of  cubic  yards  actually  placed.  When  integral  curbs  and 
gutters  are  constructed  and  a  square  yard  basis  is  used, 
their  surface  areas  are  included,  but  no  allowance  is  made 
for  extra  thickness,  as  the  bid  price  is  supposed  to  include 
this  item.  The  same  is  true  of  reinforcement  and  expansion 


140 


120 


o 

LJ 

o: 
O 
C3 

<   60 

a 

a: 

g 

o 

,,     40 


3:6 
2# 

1:2:4 


1:2:3 


10  15  20  25 

AREA  OF  END  SECTION,  Sw.  FT. 


30 


Fig.  24     Coarse  Aggregate  Required  for  Concrete  Construction 

joint  materials.  The  Inspector  should,  of  course,  make 
measurements  of  length,  width  and  depth  of  concrete  but 
in  addition  should  keep  track  of  the  actual  and  relative 
volumes  of  the  constituents  of  the  mix,  both  as  a  check  on 
linear  measurements  and  upon  proportions  used.  For  this 
purpose  Figs.  24  and  25  will  prove  useful.  In  concrete  foun- 


182     Concrete  Foundations  and  Pavements 


dations  and  pavements  the  thickness  of  concrete  through- 
out the  width  of  the  structure  is  seldom  uniform,  nor  have 


ce 
S 
E  50 


40 


30 


9n 
20 


o  10 


10  15  20  25 

AREA  OF  END  SECTION.  SQ.  FT. 


1:2:3 

1:3:6 

1:214:5 

1:2:4 

1:IV2:3 


800 


700 


600  z 


8 


500^ 


GS  OF^ 


BA 


200 


30 


5 
Fig.  25    Fine  Aggregate  and  Cement  Required  for  Concrete 


Construction 


any  general  standards  been  adopted  relative  to  thickness  or 
crowns  for  different  widths.    The  diagrams,  therefore,  show 


Materials 


183 


the  number  of  cubic  yards  of  coarse  aggregate  and  fine 
aggregate  and  the  number  of  bags  of  cement  for  each  100 
linear  feet  of  structure  for  various  end  section  areas  in  the 
case  of  five  common  proportions.  To  use  these  diagrams  in 
connection  with  field  work  it  will  be  necessary  to  ascertain 
from  the  plans  what  the  area  of  the  typical  end  section 
actually  is  or  if  the  crown  of  subgrade  and  surface  is 
known  to  first  calculate  the  area  of  the  end  section  (§  360). 
In  these  diagrams  the  stone  is  assumed  to  contain  45  per 
cent  voids,  and  as  in  practical  work  over  45  per  cent  by 
volume  of  mortar  is  used  in  the  concrete  there  is  always  less 
than  one  cubic  yard  of  stone  in  a  cubic  yard  of  concrete. 
The  quantities  have  been  calculated  from  the  following 
values  as  given  by  Taylor  &  Thompson.1 

QUANTITIES  OF  CONSTITUENTS  IN  ONE  CUBIC  YARD  OF  CONCRETE 


Proportions 

Cement 
sacks 

Sand 
eu.  yds. 

Stone 
cu.  yds. 

1:  1£:3 

8.00 

0.42 

0.84 

1:2:3 

7.24 

0.51 

0.76 

1:2:4 

6.28 

0.44 

0.88 

1:2£:5 

5.20 

0.46 

0.92 

1:3:6 

4.44 

0.47 

0.94 

230.  Sampling,  (a)  Cement  should  invariably  be 
sampled,  and  tested  in  the  laboratory,  prior  to  its  use 
(§§  85,  86)  by  methods  already  described.  Preliminary 
samples  of  coarse  and  fine  aggregate  should  also  be  taken 
and  submitted  to  the  laboratory,  particularly  in  connection 
with  quality  and  mortar  strength  tests.  (For  sampling 
broken  stone  and  broken  slag  see  §§  38  to  40  and  172; 
for  gravel  see  §§  59,  60  and  153;  and  for  sand  or  other 
fine  aggregate  see  §§  59  and  60.)  Size  or  grading  tests  of 
both  coarse  and  fine  aggregates  should  be  made  throughout 
1  Concrete  Plain  and  Reinforced,  John  Wiley  &  Sons.  Inc. 


184     Concrete  Foundations  and  Pavements 

the  work  (§371)  and  also  determinations  of  weight  per 
cubic  foot  (§375),  if  required.  Cement  samples  should 
weigh  about  10  pounds  each  and  be  shipped  in  air-tight 
containers.  Both  coarse  and  fine  aggregate  samples  should 
be  shipped  in  close- woven  cloth  bags  or  tight  boxes.  The 
weight  of  coarse  aggregate  samples  should  depend  upon 
the  maximum  size  of  particles  present  (§  153a).  Fine  aggre- 
gate samples  should  ordinarily  weigh  10  pounds. 

(b)  During  use  at  least  one  sample  of  coarse    and  fine 
aggregate  should  be  tested  by  the  Inspector  from  each  bulk 
shipment   (§§  40,   60c) .     In  addition  one    sample    of    both 
should  be  tested  for  every  1000  square  yards  of  foundation 
work  and  for  every  500  square  yards  of  pavement.    If  slag 
is  used,  weight  per  cubic  foot  determinations,  if  required, 
should  be  made  when  sampling  for  size  or  grading. 

(c)  A  sample  of  each  shipment  of  expansion  joint  material 
(§§329,  330),  metal  reinforcing  (§342)  and  hydrated  lime 
(§  226)  should  be  submitted  to  the  laboratory  unless  sampled 
and  tested  prior  to  shipment.     In  addition  samples  of  the 
concrete  actually  used  are  sometimes  required  for  laborar 
tory  strength  tests.     When  this  is  so,  •  suitable  forms  or 
molds,  of  stiff  pasteboard  or  steel,  are   furnished   the   In- 
spector.   Thus,  the  New  York  State  Highway  Commission 
requires  that  two  specimens  be  prepared  for  each  500  cubic 
yards  of  concrete.     Samples  used  in  preparing  these  speci- 
mens are  taken  at  random  from  the  batches  used  and  are 
molded  at  the  time  and  place  of  mixing.    The  samples  are 
allowed  to  remain  in  the  molds  for  two  days  and  are  then 
aged  for  19  days  under  the  same  conditions  as  the  concrete 
structure.    On  the  21st  day  they  are  shipped  to  the  labora- 
tory in  a  box  properly  protected  from  breakage.    Such  speci- 
mens should  be  marked  for  identification  and  should  be 
accompanied   by   information   giving   the  location   on   the 
work  from  which  they  were  taken,  proportions  of  the  mix, 
method  of  curing,  etc. 


Maintenance  of  Concrete  Pavements     185 

MAINTENANCE  OF  CONCRETE  PAVEMENTS 

231.  Methods,  (a)  The  earliest  disintegration  of  prop- 
erly designed  and  well-constructed  concrete  pavements  is 
usually  in  connection  with  the  formation  of  cracks  and 
spalling  at  both  cracks  and  joints.  Maintenance  then  con- 
sists in  filling  such  places  with  hot  bituminous  material  and 
covering  with  coarse  dry  sand.  Prior  to  filling,  cracks  should 
be  cleaned  as  thoroughly  as  possible.  For  cleaning  fine 
cracks,  the  Committee  on  Roads  and  pavements  of  the 
American  Concrete  Institute  recommend  the  use  of  an 
automobile  tire  pump.  In  the  case  of  joints,  the  old  joint 
material  is  sometimes  removed  for  a  depth  of  \  to  \  inch 
before  the  new  bituminous  material  is  poured.  When  pour- 
ing the  bituminous  material,  care  should  be  taken  to  pre- 
vent its  overflow  for  a  width  of  more  than  one  or  two  inches 
and  a  narrow  spout  pouring  pot  should  be  used  for  this 
purpose. 

(b)  Slight  depressions  are  remedied  by  thorough  cleaning 
followed  by  the  application  of  bituminous  material  such  as 
used  in  surface  treatments  (§  183)  and  a  covering  of  sand, 
care  being  taken  to  use  no  more  material  than  is  required 
to    bring   the    patch   flush   with   the   surrounding   surface. 
Pockets  and  deeper  depressions  are  remedied  by  thorough 
cleaning  and  painting  with  bituminous  material  and  filling 
with  a  cold   mix   bituminous   aggregate   (§§  333,  334)  the 
particles  of  which  are  usually  between  J  and  \  inch  in  diame- 
ter.    Such  mixtures  should  be  tamped  into  place  and  covered 
with  coarse  sand.     Sometimes  the  repair  is  made  by  first 
filling  the  clean  hole  with  the  aggregate  and  pouring  on 
the  bituminous  material. 

(c)  In  the  case  of  replacements,  due  to  holes  cut  through 
the  entire  thickness  of  the  concrete  slab,  the  subgrade  should 
consist  of  sound  material  thoroughly  rammed  into   place. 
Any  accumulation  of  water  should  first  be  removed.     The 
sides  of  the  cut  should  be  cleaned  and  painted  with  a  mix- 


186     Concrete  Foundations  and  Pavements 

ture  of  neat  cement  and  water  just  prior  to  filling  with  con- 
crete. The  concrete  for  small  repairs  is  usually  mixed  by 
hand  to  a  somewhat  stiffer  consistency  than  that  used  in 
original  construction.  It  should  be  well  tamped  into  place 
until  the  tamping  brings  free  water  to  the  surface.  The 
patched  area  should  then  be  struck  true  to  the  surrounding 
surface.  The  new  concrete  should  be  kept  moist  for  four 
or  five  days  and  protected  from  traffic  for  at  least 
10  days. 

(d)  Concrete  pavements  are  sometimes  protected  by  sur- 
face treatment  with  bituminous  materials  (§  183).  When  a 
concrete  pavement  becomes  so  worn  as  to  require  resur- 
facing it  is  usually  made  to  serve  as  foundation  for  some 
other  type  of  pavement.  If,  however,  it  is  to  be  resurfaced 
with  concrete  the  old  pavement  should  first  be  thoroughly 
cleaned  and  brushed  with  wet  grout  just  ahead  of  placing 
the  new  wearing  course  which  should  be  laid  as  described 
under  original  construction.  In  such  case  joints  in  the 
new  course  should  be  placed  directly  over  those  in  the  old 
pavement.  The  Committee  on  Concrete  Roads  and  Pave- 
ments of  the  American  Concrete  Institute  has  recommended 
that  the  resurfacing  course  should  be  not  less  than  3  inches 
thick  and  should  carry  reinforcement  in  the  middle  of  the 
layer. 

232.  Inspection.     Inspection  of  maintenance  will  usually 
be  the  same  .as  for  surface  treatment  (§§  179-187)  or  patch- 
ing bituminous  roads  (§  207) .     In  cases  involving  replace- 
ment or  resurfacing  with  concrete,  it  should  be  the  same 
as  for  original  construction,  in  which  case  the  extent   of 
sampling  and  testing  should  depend  upon  the  amount  of 
work  and  materials  involved. 

i  •)')• 

INSPECTOR'S  EQUIPMENT 

233.  Construction.     The  Inspector  should  ordinarily  be 
equipped  with  the  following  articles: 


Inspector's  Equipment  187 

For  Measurements: 
A  50-foot  steel  tape. 
A  pocket  rule  (§  387). 

A  1-cubic-foot  box  (should  ordinarily  be  furnished  by 
the  contractor,  together  with  paint  and  brush  for 

gauging  wheelbarrows). 

• 

For  Sampling: 

A  supply  of  close-woven  bags  of  suitable  size  for  coarse 

and  fine  aggregates. 
A  ball  of  stout  twine. 

A  supply  of  eyelet  tags  for  identification  information. 
A  few  1-quart  tin  cans  with  tight-fitting  covers. 
A  supply  of  gum  labels. 
A  supply  of  concrete  molds  if  samples  of  cement  are 

required. 

For  Testing: 

A  hand  sample  of  approved  rock  for  visual  comparison, 
if  broken  stone  is  used. 

A  set  of  field  screens  and  sieves  with  suitable  openings 
as  may  be  covered  in  specifications  for  size  and  grad- 
ing. Screen  openings  of  3",  l\"  and  J"  are  suggested 
for  coarse  aggregates  for  foundations.  Openings  of 
2",  I"  and  \"  are  suggested  for  coarse  aggregates  for 
pavements.  For  fine  aggregates  20-,  50-  and  100- 
mesh  sieves  are  suggested  (§371). 

A  spring  balance  with  pan  capacity  of  10  pounds  (§  371). 

A  spring  balance  with  pan  capacity  of  200  grams  (§  371). 

A  100-c.c.  glass  cylinder  for  volumetric  silt  testing 
(§  373)  may  be  found  useful. 

A  3  per  cent  solution  of  sodium  hydroxide  and  a  12- 
ounce  graduated  prescription  bottle  may  be  found 
useful  for  detecting  organic  impurities  (§372). 

A  small  pocket  magnifying  glass  may  also  prove  useful. 

A  thermometer,  if  heated  bituminous  material  is  to  be 
used  in  expansion  joints  (§386). 


188     Concrete  Foundations  and  Pavements 

For  Records  and  Reports: 
A  field  diary  and  pencil. 
A  supply  of  report  forms  (§  404) . 
A  carbon  paper  for  duplication  of  reports. 

234.  Maintenance.  For  maintenance  with  bituminous 
materials  the  Inspector's  equipment  will  ordinarily  be  the 
same  as  for  surface  treatment  (§  191).  For  extensive  re- 
placements or  resurfacing  with  concrete  it  should  be  the 
same  as  for  original  construction  (§  233). 


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I 


. 
CHAPTER  XII 

BITUMINOUS  PAVING  PLANT 
INSPECTION 

PAVING  PLANTS 

235.  Function  of  Paving  Plants.  The  function  of  a  pav- 
ing plant  is  to  manufacture,  from  mineral  aggregate  and 
bituminous  material,  a  hot  paving  mixture  or  composition 
which  will  be  delivered  upon  the  road  as  a  finished  product, 
under  such  conditions  that  it  may  immediately  be  spread 
to  the  desired  thickness  and  compacted  by  rolling.  Paving 
plant  operations  may,  in  a  sense,  be  considered  independent 
of  the  actual  pavement  construction,  but  there  are  several 
important  factors  that  make  it  necessary  for  plant  work 
and  construction  work  to  proceed  simultaneously  and  to 
regulate  one  another  to  a  considerable  extent.  It  is,  there- 
fore, desirable  that  the  paving  plant  be  located  as  near  as 
possible  to  the  site  of  construction.  A  bituminous  mixture 
unless  first  molded  into  blocks  (§315)  must  be  delivered  to 
the  road  at  such  temperature  that  it  may  be  readily  spread. 
As  such  mixtures  set  up  upon  cooling,  this  means  that  the 
plant  should  produce  and  deliver  material  no  faster  than, 
and  only  at  such  times  as,  it  can  be  immediately  laid.  On 
the  other  hand,  the  plant's  output  capacity  is  known  and, 
as  construction  work  is  planned  accordingly,  the  plant  can- 
not at  will  work  intermittently  when  called  upon  to  supply 
mix  without  seriously  interfering  with  the  construction 
work  and  causing  unnecessary  expense.  Moreover,  the 
behavior  of  the  bituminous  mixture,  when  being  spread  or 
compacted,  may  indicate  the  desirability  of  slight  modifica- 

189 


190      Bituminous  Paving  Plant  Inspection 

tions  in  the  proportioning  of  constituents  which  are  usually 
allowable  under  specification  requirements.  The  closest 
cooperation  should  therefore  exist  between  plant  and  pave- 
ment work  and  the  inspection  of  both. 

236.  Duties-  of   Plant   Inspector.     The    plant    inspector 
should  have  had  sufficient  experience  to  suggest  modifica- 
tions of  proportions  within  specification  requirements,  which 
from  time  to  time  it  may  be  desirable  to  make  in  order  to 
produce  a  suitable  and  uniform  product.     He  should  care- 
fully observe  all  details  of  plant  operation,  particularly  in 
connection  with  the  heating  of  the  individual  constituents, 
their  measurement  or  proportioning,  the  period  of  mixing 
and  the  condition  of  the  mix  upon  leaving  the  plant.     He 
should  keep  a  record  of  the  temperatures  to  which  both  the 
bituminous  material  and  the  mineral  aggregates  are  heated 
prior  to  mixing  and  the  temperature  of  the  finished  mixture 
when  discharged.    He  should  test  and  record  the  consistency 
(§§  378,  379)  of  the  bituminous  material  used,  particularly 
if  fluxing  is  carried  on  at  the  plant,  in  which  case  he  should 
see  that  the  proper  proportions  of  asphalt  and  flux  are  used 
and  that  a  uniform  product  is  obtained.     He  should  make 
grading  tests  (§  371)  of  the  mineral  aggregate  constituents 
and  see  that  at  all  times  proper  proportions  of  bitumen  and 
aggregate  are  being  used.     He  should  see  that  weight  or 
volume  measurements  are  checked  from  time  to  time.     In 
addition  he  should  test  (§  380)  certain  types  of  mix  to  ascer- 
tain if  the  proportions  are  such  as  to  produce  a  satisfactory 
product  when  laid  and  compacted.    He  should,  as  required, 
forward  to  the  laboratory  samples  of  the  various  constitu- 
ents and  of  the  mix  itself  for  check  and  control  tests.    He 
may  ateb  at  times  be  required  to  prospect    for  available 
sources  of  supply  in  connection  with  sand  which  may  be 
used  in  the  aggregate. 

237.  Types  of  Plants,     (a)  Bituminous  paving  plants  as 
here    considered    are    complete    installations    for    heating, 
measuring  or  weighing,  and  combining  all  of  the  constitu- 


Paving  Plants  191 

ents  of  a  bituminous  mix.  Hand  mixing  and  the  use  of 
concrete  mixers,  with  or  without  heating  devices,  in  the 
preparation  of  certain  classes  of  bituminous  concrete  are 
considered  elsewhere  (§§333,  334).  There  are  three  types 
of  plants,  all  of  which,  however,  operate  along  the  same 
general  lines.  These  are  the  permanent  or  stationary,  the 
semi-portable  and  the  portable  plant.  The  permanent 
plant  is  mainly  used  in  connection  with  the  construction 
and  maintenance  of  city  pavements  and  is  frequently  owned 
and  operated  by  the  municipality.  As  it  is  only  to  be  used 
in  supplying  material  for  a  restricted  locality,  and  porta- 
bility is  not  a  necessary  feature,  the  settings  are  usually 
stationary  and  its  design  may  involve  heavier  and  more 
substantial  equipment  than  for  the  other  two  types.  The 
portable  is  of  lighter  construction  and  frequently  of  smaller 
capacity.  It  is  constructed  in  two,  and  sometimes  in  three, 
units  to  facilitate  moving  it  from  place  to  place.  Such  plants 
are  commonly  used  by  contractors  for  relatively  small 
isolated  jobs  where  the  plant  may  be  operated  at,  or  ad- 
jacent to,  the  site  of  work,  and  frequently  moved  along  with 
the  work.  Semi-portable  plants  are  of  heavier  construction 
but  may  be  moved  from  place  to  place  by  rail.  They  are 
sometimes  called  railroad  plants  and  are  most  conveniently 
set  up  and  operated  near  a  railroad  siding.  They  are  largely 
used  by  contractors  for  municipal  work  and  in  other  locali- 
ties where  the  yardage  of  construction  warrants  and  rail 
facilities  are  sufficiently  close  to  the  work.  Such  plants  are 
often  given  a  more  or  less  permanent  position  and  set  up 
in  connection  with  municipal  work. 

(6)  Some  paving  plants  are  designed  to  turn  out  only  a 
single  type  of  product,  in  which  case  certain  parts  of  a  gen- 
eral paving  plant  may  be  eliminated.  Considering  all  types 
of  bituminous  mixtures  used  in  highway  construction  with 
the  exception  of  asphalt  block  (§  315),  the  following  ma- 
chinery and  equipment  may  be  present  in  addition  to  the 
power  and  heating  plant.  An  elevator,  usually  of  the  belt- 


192     Bituminous  Paving  Plant  Inspection 

and-bucket  type,  is  employed  to  carry  the  mineral  aggregate 
to  a  drier  or  heating  drum,  but  where  the  aggregate  is  to 
be  heated  as  a  batch,  the  measured  material  for  each  batch 
may  be  elevated  directly  to  a  storage  bin,  which  discharges 
into  the  drier.  In  the  first  case  a  more  or  less  continuous 
stream  of  heated  aggregate  is  discharged  into  an  elevator 
which  lifts  it  to  a  hot  storage  bin,  while  in  the  second  it  is 
discharged  directly  into  the  mixer.  The  hot  storage  bin  is 
sometimes  divided  into  compartments  and  a  rotary  screen 
introduced  between  the  drier  and  bin  in  order  to  separate 
the  hot  aggregate  into  two  or  more  sizes.  From  the  hot 
storage  bin  the  aggregate  is  discharged  into  a  measuring  box 
from  which  it  is  emptied  into  the  mixer.  In  any  event,  after 
the  aggregate  has  entered  the  mixer  a  measured  or  weighed 
amount  of  heated  bituminous  cement  is  also  introduced,  and 
when  the  mixing  is  completed  the  finished  product  is  dis- 
charged directly  into  wagons  or  wheel  barrows.  If  a  min- 
eral filler  is  to  be  incorporated  in  the  mix  it  is  measured  cold 
either  in  buckets  or  by  a  box  device  similar  to  that  used  for 
the  main  aggregate.  The  bituminous  material  equipment 
may  include  a  hoist  for  lifting  the  material  to  the  melting 
tank,  or  tanks,  where  it  is  rendered  fluid  by  the  application  of 
heat.  If  it  is  not  to  be  fluxed  it  is  drawn  or  lifted  by  a  special 
device  directly  from  the  melting  tank  to  a  measuring  or 
weighing  bucket  which  empties  into  the  mixer.  If  fluxing 
is  involved,  a  tank  for  holding  flux  oil  should  be  supplied, 
together  with  means  for  measuring  the  amount  drawn  into 
the  melting  kettle  in  which  the  fluxing  is  then  conducted. 
From  the  melting  tank  the  fluxed  material  is  led  into  a 
draw-off  tank  of  equal  capacity  and  afterwards  lifted  to  the 
weighing  bucket. 

PLANT   OPERATION 

238.  Storage  of  Materials.  As  received  at  the  plant, 
mineral  aggregate  for  bituminous  mixtures  is  stored  in  piles, 
as  near  as  possible  to  the  elevator  which  is  to  convey  it  to 


Plant  Operation  193 

the  drier  or  heater.  It  is  frequently  necessary  to  combine 
two  or  more  sizes  or  grades  of  aggregate,  in  which  case  the 
different  sizes  or  grades  should  be  kept  in  separate  piles. 
All  aggregate  should  be  stored  so  that  it  will  not  become 
mixed  with  dirt  or  other  foreign  material.  Storage  bins, 
in  the  plant  proper,  are  of  relatively  small  capacity  and 
are  intended  for  use  only  during  its  operation.  Bituminous 
cements  and  fluxes  are  usually  stored  in  barrels  or  drums 
(§92)  except  in  the  case  of  the  more  permanent  set-ups 
where  material  may  be  purchased  by  the  tank  car  and  trans- 
ferred to  large  storage  tanks  until  used. 

239.  Heating  Mineral  Aggregates.     The  mineral  aggre- 
gate is  ordinarily  dried  and  heated  by  passing  it  through 
a  revolving  metal  drum  which  is  heated  from  the  outside 
and  through  which  a  constant  stream  of  hot  air  or  hot 
exhaust  gases  are  forced.     As  it  passes  through  the  drum 
the  aggregate  is  thrown  about  by  means  of  baffle  plates,  or 
other  device,  so  that  it  is  not  only  heated  by  contact  with 
the  hot  metal  but  also  dried  by  intimate  contact  with  the 
current  of  hot  air  or  gases.     A  pyrometer  is  sometimes 
placed  at  the  exhaust  end  to  register  the  temperature  of  the 
aggregate  as  it  passes  the  drum.     The  exhaust  gases  fre- 
quently remove  considerable  dust  from  the  aggregate  and 
are,  therefore,  sometimes  passed  through  a  dust  collector. 
For  this  reason  mineral  filler  when 'used  is  not  ordinarily 
preheated.    When  two  or  more  grades  or  sizes  of  aggregate 
are  to  be  combined,  they  are  usually  fed  simultaneously  to 
the  mixer  in  the  proper  volumetric  proportions,  being  meas- 
ured  by  shovels   or   wheelbarrows.     If,  however,  the   hot 
aggregate  is  to  be  separated  before  passing  to  the  hot  storage 
bin,  no  attempt  need  be  made  to  proportion  the  sizes  before 
they  enter  the  drier  other  than  to  regulate  their  feed  so 
that  the  storage  bin  will  always  contain  a  sufficient  quantity 
of  each  size  to  produce  a  batch. 

240.  Separating  the  Aggregate.     Segregation  of  sizes  is 
very  apt  to  occur  during  passage  through  the  drier.     This 


194      Bituminous  Paving  Plant  Inspection 

is  particularly  true  in  the  case  of  mixtures  of  coarse  and 
fine  aggregate  such  as  a  mixture  of  broken  stone,  with  frag- 
ments over  ^  inch  in  diameter,  and  sand.  In  such  cases, 
therefore,  it  is  advisable  to  pass  the  output  of  the  drier 
through  a  rotary  screen  so  as  to  separate  it  into  suitable 
sizes  which  are  held  in  separate  compartments  of  the  hot 
storage  bin.  In  some  plants  this  procedure  is  unnecessary 
if  each  mixing  batch  of  aggregate  is  heated  and  dried  sepa- 
rately. Even  in  the  case  of  sand  mixtures,  however,  a  screen 
is  often  used  to  throw  out  all  particles  above  a  certain 
diameter. 

241.  Heating  and  Fluxing  Bituminous  Materials.  Melt- 
ing and  fluxing  tanks  are  heated  either  by  direct  fire  or 
by  means  of  steam  coils,  preferably  the  latter.  For  general 
use  they  should  be  provided  with  an  agitating  device  to 
prevent  settlement  of  any  nonbituminous  constituent 
which  may  be  present  in  the  bituminous  material  and  to 
assist  in  fluxing.  Agitation  is  secured  either  by  a  mechanical 
device  or  by  means  of  steam  or  air  jets  forced  up  through 
the  heated  material  from  coils  placed  in  the  bottom  of  the 
tank.  The  fluxing  process  usually,  consists  of  combining 
refined  asphalt  (§  96)  with  a  petroleum  residuum  or  flux 
(§  95)  in^  such  proportions  as  to  produce  an  asphalt  cement 
of  the  desired  consistency  or  penetration.  A  measured  or 
known  quantity  of  the  refined  asphalt  is  first  placed  in  the 
fluxing  tank,  where  it  is  heated  to  a  fluid  condition.  A  meas- 
ured quantity  of  hot  flux  is  then  run  in  and  the  contents  of 
the  tank  continuously  agitated  until  asphalt  and  flux  have 
combined  to  produce  an  asphalt  cement  of  absolutely  uni- 
form consistency.  When  steam  agitation  is  used  special 
care  is  required  to  prevent  condensation  before  it  is  injected 
into  the  bituminous  material,  or  foaming  will  result.  After 
melting  or  fluxing,  the  bituminous  material  is  maintained  at 
the  proper  temperature  until  used  in  the  mix.  Tanks  should 
be  provided  with  suitable  stationary  thermometers  for 
registering  the  temperature  of  the  bituminous  material. 


Plant  Operation  195 

242.  Proportioning  the  Constituents  of  the  Mix.    Final 
proportioning  of  the  constituents  of  the  mix  is  conducted 
from  a  mixing  platform  set  above  the  "mixer.     Here  the 
main  aggregate,  the  filler  if  used,  and  the  bituminous  ma- 
terial are  measured  or  weighed  before  placing  them  in  the 
mixer.     The  mineral  aggregate  is  usually  run  from  the  hot 
storage  bin  into  a  box  where  it  is  measured,  in  some  cases 
by  volume,  but  preferably  and  more  accurately  by  weight, 
to  the  capacity  of  the  mixer.     If  it  has  previously  been 
separated  into  sizes,  each  size  is  separately  measured  in 
predetermined    proportions.      If   the     aggregate    has   been 
heated  or  stored  in  measured  batches  it  is  discharged  directly 
into  the  mixer.    Mineral  filler  may  be  measured  in  the  same 
box  as  the  rest  of  the  aggregate,  but  as  it  is  used  in  relatively 
small  quantities  it  is  usually  measured  in  hand  buckets  and 
dumped  directly  into  the  mixer.     The  hot  bituminous  ma- 
terial is  measured  in  a  bucket  preferably  by  weight.     The 
bucket  is  usually  suspended  on  trunions,  which  allows  it 
to  be  readily  moved  from  the  charging  pipe  to  the  mixer  into 
which  it  is  emptied. 

243.  Mixing.     There  are  a  number  of  types  of  mixers, 
but  the  one  most  commonly  used  consists  of  an  iron  box 
equipped  with  a  double  set  of  blades  revolving  on  two 
horizontal  shafts  extending  through  the  box.    These  blades 
are  so  set  that  the  mixture  is  continually  tossed  upward  and 
at  the  same  time  worked  toward  the  center' of  the  mixer. 
The  blades  are  spaced  so  as  to  efficiently  mix  a  given  size 
aggregate  and  are  detachable  so  that  worn  or  broken  blades 
may  be  replaced  and  different  spacing  may  be  facilitated 
by  changing  shafts.    Such  mixers  are  provided  with  a  slid- 
ing discharge  at  the  bottom  which  is  controlled  by  a  lever. 
Another  type  of  mixer  consists  of  a  revolving  drum  equipped 
with  a  central  spiral  conveyor  which  is  superimposed  with 
another  spiral  conveyor  operating  in  the  reverse  direction. 
After  all  of  the  constituents  have  been  introduced  into  the 
mixer  they  should  be  mixed  until  the  mineral  particles  are 


196     Bituminous  Paving  Plant  Inspection 

thoroughly  and  uniformly  coated  with  bituminous  material. 
The  finished  mix  is  then  dumped  into  wagons  or  wheel- 
barrows and  conveyed  directly  to  the  site  of  construction. 

244.  Transportation  of  the  Mix  to  the  Road.  It  is  essen- 
tial that  the  bituminous  mixture  be  delivered  on  the  road 
at  such  temperature  that  it  may  be  readily  spread  and  com- 
pacted. As  this  temperature  is  approximately  that  re- 
quired for  mixing,  precautions  should  be  taken  to  prevent 
rapid  cooling  of  the  mix  after  being  discharged  from  the 
mixer.  If  the  construction  work  is  at  any  considerable  dis- 
tance from  the  plant,  each  load  should  be  protected  while 
in  transit  by  a  canvas  cover.  Carts,  trucks  or  wagons  used 
for  transporting  the  mix  should  preferably  be  provided 
with  sheet  metal  linings.  If  not,  they  .should  be  kept  white- 
washed or  oiled  on  the  inside  to  prevent  the  mix  from  stick- 
ing to  them  when  dumped  on  the  road. 


INSPECTION  DETAI^ 

245.  Characteristics  of  Mineral  Constituents,  (a)  The 
plant  Inspector  is  not  expected  to  make  tests  of  quality  of 
the  mineral  constituents  which  may  be  covered  in  specifica- 
tions, as  such  tests  are  made  by  the  laboratory.  Visual 
examination  should  be  made,  however,  in  connection  with 
certain  physical  characteristics  of  the  various  products. 
If  broken  stone  is  to  be  used,  the  rock  is  usually  approved 
upon  laboratory  tests  made  in  advance  of  the  work,  in  which 
case  the  Inspector  will  find  it  convenient  to  secure  a  hand 
specimen  from  the  sample  tested  to  visually  compare  with 
material  furnished.  In  the  case  of  slag,  if  the  weight  per 
cubic  foot  is  specified,  a  determination  of  this  property 
(§  375)  should  be  made  on  a  sample  from  each  shipment, 
or,  if  delivered  in  wagons,  for  approximately  each  50  cubic 
yards.  The  quality  of  gravel  pebbles  should  be  tested  from 
time  to  time  by  means  of  a  hammer  (§  374)  .  All  aggregates 
should  be  examined  to  see  that  they  are  free  from  dirt  or 


Inspection  Details  197 

extraneous  material  and  thin  splintery  fragments,  and  that 
the  individual  particles  are  not  covered  with  a  coating  of 
slay  or  loam  which  will  prevent  proper  adhesion  of  the 
bituminous  cement  to  their  surfaces.  Sand  should  be 
examined  to  see  that  it  is  composed  of  hard  reasonably 
sharp  quartz  grains. 

(6)  Size  or  grading  tests  (§  371)  should  be  made  on 
samples  taken  from  each  shipment  of  aggregate  and  if 
marked  variations  occur  between  different  shipments  of 
presumably  the  same  product  they  should  be  stored  in 
separate  piles.  If  the  mineral  constituents  are  delivered 
by  wagons  a  sample  should  be  tested  for  grading  for  approxi- 
mately each  50  cubic  yards  received. 

246.  Consistency  and  Bitumen  Content  of  Bituminous 
Material,  (a)  The  only  test  of  bituminous  cement  which 
the  Inspector  is  required  to  make  is  that  of  consistency. 
In  the  case  of  refined  tar  the  float  test  (§  379)  is  used,  and 
in  the  case  of  asphalt  and  asphalt  cements  the  penetration 
test  (§  378)  is  used.  Representative  samples  from  each 
shipment  of  bituminous  cement  should  be  tested  for  con- 
formity with  the  specification  requirement  for  consistency 
immediately  upon  its  arrival.  In  addition,  a  test  for  con- 
sistency should  be  made  early  in  the  morning  upon  each 
tank  of  melted  material  which  has  been  heated  over  night. 
Prolonged  heating,  particularly  if  accompanied  by  violent 
agitation,  may  materially  harden  the  product.  For  this 
reason  low  heat  and  gentle  agitation  is  advisable  when  the 
melted  material  is  being  carried  over  from  one  day's  work 
to  another. 

(6)  When  refined  asphalt  is  to  be  fluxed  at  the  plant  it 
is  necessary  to  ascertain  to  what  extent  the  addition  of  a 
given  proportion  of  flux  will  increase  the  penetration  of  the 
asphalt.  This  will  largely  depend  upon  the  relative  con- 
sistency of  asphalt  and  flux  and  no  definite  rule  can  be 
given  which  is  applicable  to  all  cases.  Proportions  are 
expressed  in  pounds  of  flux  per  100  of  R.A.  (refined  asphalt), 


198      Bituminous  Paving  Plant  Inspection 

and  for  those  products  ordinarily  handled  at  a  paving  plant 
it  will  usually  be  found  that  one  pound  of  flux  will  increase 
the  penetration  of  100  pounds  of  R.A.  from  2  to  4  points. 
In  general,  the  harder  the  R.A  and  the  more  viscous  the 
flux,  the  greater  will  be  the  proportion  of  flux  required  to 
produce  an  A.C.  (asphalt  cement)  of  given  penetration.  A 
fluxing  curve  such  as  shown  in  Fig.  26  will  be  found  useful 
as  a  guide  to  regulating  proportions  of  A.C.  and  flux. 

Such  a  curve  should  be  obtained  from  the  laboratory  or 
made  by  the  Inspector  from  penetration  tests  upon  small 


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DN  OF  A.C. 

of  Fluxing  Curve 

amples  of  A.C.  prepared  by  combining  different  propor- 
tions of  R.A.  and  flux.  The  penetrations  of  A.C.  'are  plotted 
against  the  proportion  of  flux  and  R.A.  and  when  connected 
by  a  continuous  line  indicate  what  penetrations  may  be 
expected  from  intermediate  proportions.  Owing  to  differ- 
ent hardening  conditions  during  the  fluxing  process  in  the 
plant  and  on  small  laboratory  samples,  such  a  curve  may 
not  give  absolutely  correct  values  for  plant  control,  but  a 
rather  definite  relation  may  be  established  after  a  few  com- 
parisons have  been  made. 


Inspection  Details  199 

(c)  When  fluxing  at  the  plant  it  is  necessary  to  keep  track 
of  the  weight  of  melted  asphalt  in  the  tank.  The  weight 
per  gallon  of  flux  should  also  be  ascertained  either  by  direct 
test  or  from  a  report  of  its  specific  gravity  (Fig.  7)  when 
the  proportion  of  flux  is  to  be  measured  by  volume  rather 
than  by  weight.  If  a  fluxing  curve  is  available  the  proper 
proportions  of  flux  is  at  once  indicated.  If  not,  a  trial  will 
have  to  be  made.  Thus  it  may  be  assumed  that  one  pound 
of  flux  will  increase  the  penetration  of  100  pounds  of  R.A. 
3  points.  If  it  is  desired  to  raise  the  penetration  of  the 
asphalt  18  points,  then  ^  or  6  pounds  of  flux  will  be  added 
to  each  100  pounds  of  R.A.  After  thorough  combination 
the  resulting  A.C.  should  be  tested  for  penetration.  The 
average  increase  in  penetration  actually  produced  by  each 
pound  of  flux  per  100  pounds  of  R.A.  should  then  be  ascer- 
tained. For  this  purpose  the  following  formula  may  be 
used,  where  x  equals  the  increase  in  penetration  produced 
by  1  pound  of  flux  to  100  pounds  of  R.A.,  a  equals  the  num- 
ber of  pounds  of  R.A.  in  the  tank,  b  equals  the  pounds  of  flux 
which  was  added,  c  represents  the  penetration  of  the  original 
R.A.,  and  d  the  penetration  of  the  resulting  A.C. 

_  a(d  -  c) 
1006 

The  value  of  x  thus  determined  may  be  used  to  ascertain 
the  amount  of  flux  required  to  prepare  new  batches  by 
means  of  the  following  formulas  in  which  the  letters  a,  b 
and  c  represent  the  same  factors  as  in  the  preceding  formula 
and  e  equals  the  desired  penetration. 

Pounds  of  flux  required  = 


If  the  trial  operation  produces  an  A.C.  of  lower  penetra- 
tion than  desired,  then  more  flux  should  be  added.  If  on  the 
other  hand  the  resulting  A.C.  is  too  soft  more  R.A.  must 
be  added  to  the  contents  of  the  tank.  The  following  formu- 
las may  be  used  to  correct  the  trial  batch  if  the  desired 


200      Bituminous  Paving  Plant  Inspection 

penetration  was  not  secured.    In  each  of  these  formulas  the 

letters  represent  the  same  factors  as  in  the  preceding  formulas : 

When  penetration  of  the  trial  batch  is  too  low,  additional 

pounds  of  flux  required  =      , 
When  penetration  of  .the  trial  batch  is  too  high  additional 

pounds  of  R.A.  required  = 

e  —  c 

(d)  When   sampling  newly  fluxed  asphalt  it  should  be 
remembered   that    considerable   time  may  be   required   to 
effect  complete  combination,  particularly  if  the  R.A.  has  a 
very  low  penetration.     In  a  paving  plant  the  main  fluxing 
operation  is  usually  conducted  at  the  end  of  a  day's  work 
and   a   sample   taken   and   tested   the   following   morning. 
Slight  corrections  in  consistency  usually  require  a  half  hour 
or  so  to  complete,  but  if  any  doubt  exists  regarding  the  com- 
pletion of  the  fluxing  process  it  is  well  to  test  the  consistency 
of  two  samples  taken  from  the  tank  at  different  levels.    In 
case  the  product  contains  a  considerable  amount  of  non- 
bituminous  material,  thorough  agitation  is  necessary  to  pre- 
vent settlement  not  only  through  the  fluxing  process,  but 
while  it  is  being  withdrawn  for  use.    In  such  cases  it  is  ad- 
visable to  occasionally  test  samples  from  different  levels  in 
the  tank  to  determine  if  the  product  is  of  uniform  consist- 
ency and  is,  therefore,  approximately  uniform  in  composi- 
tion.   If  not,  more  active  agitation  is  required. 

(e)  When  an  oil  asphalt  is  fluxed  the  amount  of  bitumen 
in  the  A.C.  maybe  considered  as  100  per  cent,  as  both  R.A. 
and  flux  consist  of  practically  pure  bitumen.     When  a  re- 
fined native  asphalt  is  fluxed,  however,  it  is  necessary  to 
consider  the   percentage  of   nonbituminous  material  which 
it  contains  in  order  to  ascertain  the  percentage  of  bitumen 
in  the  resulting  A.C.     This  may  be  determined  by  means 
of  the  following  formula,  in  which  x  equals  the  per  cent  of 


Inspection  Details  201 

bitumen  in  the  A. C.,  p  equals  the  per  cent  of  bitumen  in  the 
R.A.,  and  a  equals  the  pounds  of  flux  per  100  pounds  of  R.A. 


100  +  a 

247.  Control  of  Temperatures.  Temperature  control  at 
a  paving  plant  is  of  great  importance,  first  to  prevent  injury 
of  the  constituents  of  the  mix  by  overheating;  second,  to 
make  it  practicable  to  secure  a  uniform  mixture  of  such 
consistency  that  it  may  be  readily  spread  and  uniformly 
compacted  on  the  road.  The  temperature  of  the  mineral  ag- 
gregate as  it  leaves  the  drier  should  be  watched  and  special 
attention  paid  to  its  temperature  as  discharged  from  the 
hot  storage  bin.  The  temperature  to  which  the  bituminous 
material  is  heated  in  the  melting  and  drawing  off  tanks 
should  be  carefully  regulated  and  that  of  the  finished  mix, 
as  it  is  discharged  from  the  mixer  and  leaves  the  plant, 
should  be  noted  from  time  to  time.  Mineral  aggregate 
should  be  heated  sufficiently  to  thoroughly  dry  it  and  facili- 
tate the  coating  of  each  particle  with  the  requisite  amount 
of  bituminous  material,  but  not  so  high  as  to  injure  the 
bituminous  coating  or  cause  it  to  partially  drain  off  when 
dumped  from  the  mixer.  The  bituminous  cement  should 
be  heated  sufficiently  to  make  it  pour  readily,  but  not  so 
high  as  to  cause  undue  loss  by  volatilization,  hardening, 
or  burning.  The  proper  temperature  limits  to  be  observed 
vary  with  the  types  of  materials  used  and  character  of  the 
paving  composition  and  should  be  covered  by  specification 
requirements.  The  following  may,  however,  serve  as  a 
general  guide: 

Mineral  Aggregates :  Degrees  F. 

For  mixing  with  refined  tars .  . 

Coarse  aggregates  for  mixing  with  A.C 200-300 

Aggregate  passing  ¥  screen  for  mixing  with 

A  n  250-350 


202      Bituminous  Paving  Plant  Inspection 

Bituminous  Materials: 

Refined  tar 225-275 

Asphalt  Cement 275-350 

Mixtures : 

Containing  tar 150-200 

Coarse  aggregates  containing  A.C 200-300 

Aggregates  passing  J"  screen  and  containing 
A.C 250-350 

248.  Measurement  and  Control  of  Proportions,     (a)  The 

proportions  of  the  constituents  of  bituminous  mixtures  are 
sometimes  specified  upon  a  volume  basis,  but  more  frequently 
by  weight.  Volume  proportions  are  the  most  logical,  in  view 
of  common  variations  in  specific  gravity  of  the  different 
types  of  mineral  aggregates,  and  bituminous  materials 
allowed  under  a  single  specification,  but  weight  proportions 
are  the  most  accurate  to  make  and,  with  any  given  set  of 
constituents,  will  produce  the  most  uniform  mixture.  Grad- 
ings  are  always  specified  and  determined  upon  a  weight 
basis. 

(6)  The  simplest  type  of  bituminous  concrete  is  one 
composed  of  a  single  commercial  broken-stone  product  and 
asphalt  cement  or  refined  tar.  The  size  or  grading  of  such 
a  product  need  only  be  determined  upon  samples  taken 
from  shipments  received  or  from  storage  piles  at  the  plant. 
For  this  type  the  proportion  of  bituminous  material  to 
aggregate  is  often  specified  as  a  definite  range  in  gallons  per 
cubic  yard,  the  exact  quantity  to  be  as  determined  by  the 
Engineer.  The  allowable  variation  in  number  of  gallons 
per  cubic  yard  is  sufficiently  wide  to  care  for  variations  in 
the  bitumen  content  of  the  bituminous  materials  allowed 
to  be  used.  In  such  cases  the  exact  proportions  to  be  used 
for  the  materials  furnished  on  the  job  is  decided  upon  the 
appearance  of  the  mix  and  its  behavior  on  the  road  during 
spreading  and  compaction.  When  once  fixed,  volume  pro- 


Inspection  Details  203 

portions  may  be  translated  to  weight  proportions  if  desired 
and  measurement  thereafter  made  by  weight. 

(c)  A  second  type  of  bituminous  concrete  contains  an 
aggregate  composed  of  two  or  more  products  such  as  broken 
stone  and  sand,  the  grading  limitations  of  each  being  specified 
together  with  the  volume  proportions  in  which  they  are  to  be 
combined.  When  these  factors  are  properly  covered,  the  grad- 
ing of  the  combined  aggregate  need  not  be  specified  or  deter- 
mined by  the  Inspector.    He  should,  however,  make  grading 
determinations  of  the  individual  constituents  and  see  that 
they  are  used  in  such  proportions  as  are  finally  set  by  the 
Engineer;   also  that  they  are  mixed  with  the  proper  propor- 
tion of  bituminous  cement  as    covered  in    the    preceding 
paragraph. 

(d)  In  a  third  type  of  bituminous  mixture  the  grading  of 
the  main  or  total  aggregate  is  specified  without  necessary 
reference  to  the  grading  of  the  individual  products  which 
may  be  required  to  produce  the  final  aggregate.     In  such 
cases  the  Inspector  should  sample  and  test  the  aggregate 
from  the  mixing  platform  as  it  is  delivered  to  the  mixer,  at 
least  once  a  day  and  more  often  if  the  necessity  is  indicated. 
In  addition,  it  will  be  necessary  for  him  to  test  the  grading 
of  each  aggregate  constituent  so  that  they  may  be  com- 
bined in  such  proportions  as  to  produce  the  specified  grad- 
ing (§  250).    In  this  type  the  proportioning  of  the  bitumi- 
nous materials  should  always  be  made  upon  a  weight  basis 
with  due    allowance    for    nonbituminous   impurities  which 
may  be  present  so  as  to  secure  the  proper  percentage  of 
bitumen  in  the  mix. 

(e)  The  proportions  of  aggregate  and  bitumen  to  be  used 
in  a  given  mix  are  sometimes  specified  upon  a  percentage 
basis  of  the  mineral  aggregate  and  sometimes  upon  a  per- 
centage basis  of  the  combination.     The  difference  between 
these   two  methods  should  be   clearly  understood  by  the 
Inspector.    Thus,  if  bitumen  is  to  be  added  to  the  extent  of 
10  per  cent  of  the  aggregate,  then  10  pounds  of  bitumen 


204     Bituminous  Paving  Plant  Inspection 

are  added  to  each  100  pounds  of  aggregate  and  the  per- 
centage of  bitumen  in  the  mix  will  be 

«•'*;'         ;    lOoTTo  =  -091  or  9-1  per  cent" 

If  on  the  other  hand  the  mix  is  specified  to  contain  10  per 
cent  bitumen,  then  10  pounds  of  bitumen  should  be  com- 
bined with  every  90  pounds  of  aggregate  or  11.1  pounds 
with  every  100  pounds  of  aggregate.  If  the  bituminous 
material  contains  nonbituminous  impurities  and  the  per- 
centage of  bitumen  is  expressed  on  the  basis  of  the  mineral 
aggregate,  then  the  number  of  pounds  of  bituminous  ma- 
terial required  for  each  100  pounds  of  aggregate  is  obtained 
by  one  of  the  following  formulas  in  which  x  equals  the  num- 
ber of  pounds  of  bituminous  material  required  for  each  100 
pounds  of  aggregate  and  b  equals  the  per  cent  of  bitumen 
in  the  bituminous  material. 

(a)  a  =  the  per  cent  of  bitumen  required  on  the  basis  of 

the  mineral  aggregate. 
IQOa 


(2)  a  =  the  per  cent  of  bitumen  required  in  the  combined 

mixture. 
lOOa 


x 


b  -  a 


(/)  The  addition  to  the  mix  of  mineral  filler  consisting  of 
finely  pulverized  rock  or  Portland  cement  is  often  specified 
on  the  same  basis  as  for  bitumen,  described  in  the  foregoing 
paragraph.  The  effect  of  mineral  filler,  which  is  to  fill  the 
very  small  voids  and  toughen  the  mix,  is  due  to  that  portion 
which  is  sufficiently  fine  to  pass  the  200-mesh  sieve.  Its 
addition  is,  therefore,  frequently  made  upon  the  basis  of 
the  per  cent  of  material  finer  than  200  mesh  which  it  con- 
tains. Sand  particles  in  the  main  aggregate  which  pass  the 
200-mesh  sieve  are  not  usually  considered  as  filler  proper 


Inspection  Details  205 

and  may  be  ignored  in  calculations  for  the  addition  of  filler. 
The  finely  divided  mineral  matter  in  Trinidad  asphalt,  or 
the  free  carbon  in  tars  may,  however,  be  considered  as  a 
substitute  for  mineral  filler,  in  which  case  an  allowance 
should  be  made  in  calculating  filler  on  a  weight  basis.  The 
formulas  which  may  be  used  under  such  circumstances  to 
ascertain  the  number  of  pounds  of  bituminous  material  and 
mineral  filler  to  add  to  each  100  pounds  of  aggregate  are 
given  below,  where  the  letters  have  the  following  significance. 

x  =  pounds  of  bituminous  material  per  100  pounds  aggregate. 
a  =  per  cent  of  bitumen  desired  in  the  mix. 
b  =  per  cent  of  bitumen  in  bituminous  material. 
y  =  pounds  of  mineral  filler  per  100  pounds  aggregate. 
I  =  per  cent  of  filler  passing  200-mesh  desired  in  the  mix. 
ra  =  per  cent  particles  passing  200  mesh  in  filler. 

100am 


a(100  -  ra)  +  b(m  -  a  -  I) 

100[6(Z  +  a)  -  lOOa] 
y  ~~  a(100  -  ra)  +  b(m  -  a  -  I) ' 

(g)  When  weighing  the  proportions  of  the  individual  con- 
stituents of  a  mix  the  Inspector  should  see  that  the  tare 
of  both  weighing  box  and  bituminous  material  bucket  are 
accurately  obtained  and  the  tare  weight  or  balance  properly 
set,  or  added  to  the  total  weight.  Tare  weights  should  be 
checked  from  time  to  time  and,  in  the  case  of  the  bitu- 
minous material  bucket,  at  least  once  an  hour  during  use, 
owing  to  the  more  or  less  constant  accumulation  of  hard- 
ened bituminous  material.  Both  scales  and  bucket  should 
be  cleaned  every  day. 

249.  The  Combination  of  Aggregates,  (a)  In  connection 
with  proportioning  two  or  more  constituents  of  an  aggre- 
gate, it  is  desirable  to  approach  as  closely  as  possible  a 
standard  grading  which  may  either  be  stated  in  the  specifi- 
cations or  may  be  considered  as  the  average  of  the  grading 


206      Bituminous  Paving  Plant  Inspection 

limitations.     For  the  purpose  of  illustration  the  following 
table  presents  a  simple  problem: 


Require- 
ment 
No. 

Sieve  Tests 

Available 
Products 

Specifi- 
cation 
Limits 

Stand- 
ards 

A 

B 

1 

Pass.  10-mesh,  ret.  on    40  rnesh 

15 

50 

12-50 

23 

2 

"     40      "        "     "     80     " 

80 

10 

15-68 

43 

3 

tt     go      «        «     a  200     " 

5 

40 

20-40 

34 

In  this  table  are  shown  the  gradings  of  two  sands,  A  and  B, 
together  with  the  specification  limits  for  grading  which  any 
combination  of  the  two  must  meet  and  a  standard  grading 
which  should  be  approached  as  closely  as  possible.  First 
of  all,  it  should  be  noted  that  neither  sand  by  itself  comes 
entirely  within  the  specification  limits.  With  regard  to 
requirement  No.  1,  both  sands  fall  within  the  specified  limits 
and,  therefore,  any  combination  will  also  meet  the  specifi- 
cations. With  regard  to  requirement  No.  2  neither  sand 
meets  the  specification  requirements  but,  as  one  is  above 
and  one  below,  a  satisfactory  combination  is  possible.  If 
both  were  above  or  both  below,  a  combination  could  not,  of 
course,  be  made  to  fall  within  the  specifications.  With 
regard  to  requirement  No.  3,  as  one  is  below  and  one  is 
within  the  specifications,  a  satisfactory  combination  is  again 
indicated.  It  is  now  necessary  to  ascertain  the  range  in 
proportion  of  the  two  sands  which  will  fall  within  the  speci- 
fications, and  what  combination  will  most  closely  approach 
the  standard.  This  problem  may  be  solved  by  trial  propor- 
tions but  better  algebraically.  All  possible  combinations 
may  be  considered  as  consisting  of  100  parts,  and  the  pro- 
portion of  either  constituent  calculated  as  parts  per  100  of 
the  combination  as  follows:  Thus,  under  requirement  No.  1 
the  percentage  of  sand  A  in  combination  with  sand  B  re- 
quired to  give  the  standard  grading  is  calculated  from  the 
following  formula,  where  x  equals  the  number  of  parts  per 


Inspection  Details 


207 


100  of  the  combination,  a  equals  the  grading  percentage  of 
sand  A,  b  equals  the  grading  percentage  of  sand  B,  and  c 
equals  the  desired  grading  percentage  of  the  combination. 
100(c  -  6) 

a-b 
In  this  case 

100(23  -  50)  _  -  2700 
15-50 


x  = 


77.1. 


From  this  result  it  is  evident  that  77  parts  of  sand  A  and 
100  -  77  or  23  parts  of  sand  B  will  produce  under  require- 
ment No.  1  the  standard  grading  of  23.  By  applying  this 
formula  logically  to  each  of  the  specification  limits  and  to 
the  standard  grading  for  each  requirement,  it  is  possible  to 
construct  a  table  showing  the  range  in  parts  per  100  of  sand 
A  which  can  be  used  with  sand  B  and  produce  a  combination 
within  specification  limits,  and  from  this  range  it  is  possible 
to  pick  the  combination  which  will  most  closely  approach 
the  standard. 


Requirement 
No. 

Parts  of  Sand  A  per  100  Parts  Combination 

Range  within  Specifi- 
cation Limits 

.Meeting  or  Closest 
to  Standard 

» 

1 
2 
3 

0  to  100 
7  to    83 
Oto    57 

77 
47 
17 

In  connection  with  the  problem  under  consideration,  it  is 
seen  from  the  table  constructed  that  sand  A  may  be  used 
with  sand  B  to  the  extent  of  from  7  to  57  parts  per  100  of 
combination  to  meet  the  specification  requirement.  Within 
these  limits  it  is  evident  that  requirement  No.  1  of  the 
standard  cannot  be  met.  By  averaging  the  values  in  this 
table  for  the  three  standard  requirements  47  is  obtained, 
which  happens  to  meet  requirement  No.  2.  Therefore,  47 
parts  of  sand  A  and  53  parts  of  sand  B  will  meet  the  specifi- 


208     Bituminous  Paving  Plant  Inspection 

cations  requirements  and  most  closely  approach  the  stand- 
ard grading.  In  this  case  the  proportions  are  so  nearly  the 
same  that  if  measured  volumetrically  in  small  batches  the 
proportion  of  1:1  would  probably  be  used. 

(b)  It  sometimes  happens  that  no  two  available  constitu- 
ents can  be  found  to  produce  a  desired  grading,  and  a  com- 
bination of  three  constituents  may  be  necessary.  Under 
these  circumstances  the  formula  given  in  the  preceding 
paragraph  may  be  applied  to  two  of  the  products  to  obtain 
a  combination  as  close  as  possible  to  the  specification  re- 
quirements. Such  combination  is  then  considered  as  a  single 
product  and  its  combination  with  a  third  product  next  taken 
up.  Thus,  suppose  that  three  sands,  A,  B  and  C,  are  avail- 
able but  that  no  combination  of  two  sands  will  meet  the 
specifications.  Certain  requirements  may,  however,  be  met 
by  combining  sands  A  and  B  in  the  proportions  of  1 :  3.  It 
is  next  found  that  this  product  may  be  combined  with  sand 
C  in  the  proportions  of  1 :  2  so  as  to  meet  specifications.  The 
proportions  of  A :  B :  C  will  then  be  1 :  3 :  2(1  +  3)  or  1 :  3 :  8. 

250.  Characteristics  of  Mix.  The  first  consideration  in 
connection  with  a  bituminous  mixture  is  that  it  shall  be  uni- 
form. There  should  be  no  noticeable  segregation  of  any  of 
the  constituents  and  each  particle  of  aggregate  should  be 
thoroughly  coated  with  bitumen.  Uniformity  can  only  be 
secured  by  carrying  on  the  mixing  process  for  a  sufficient 
length  of  time.  The  exact  time  necessary  will  depend  upon 
the  type  of  mixer  and  its  method  of  operation.  Under 
ordinary  conditions  one  minute  will  be  required  for  aggre- 
gates containing  25  per  cent  or  more  of  material  passing  the 
10-mesh  sieve.  If  the  aggregate  is  exceedingly  fine,  as  in 
the  case  of  earth  mixtures,  1 J  to  2  minutes  may  be  required, 
while  J  minute  may  be  sufficient  for  aggregates  containing 
little  or  no  material  passing  a  10-mesh  sieve.  When  dis- 
charged from  the  mixer  the  mix  should  tend  to  crawl  but 
not  flow  or  remain  stationary  in  a  pile.  This  will  depend 
upon  its  temperature  and  the  percentage  of  bitumen  which 


Inspection  Details  209 

it  carries.  If  the  mix  is  sloppy,  either  too  high  a  temperature 
or  too  much  bitumen  is  indicated.  If  stiff,  dry,  and  luster- 
less  in  appearance  a  deficiency  of  bitumen  should  be  sus- 
pected unless  marked  overheating  has  occurred,  in  which 
case  it  may  evolve  blue  or  yellowish  fumes  according  to 
whether  an  asphalt  or  tar  binder  has  been  used.  The  tem- 
perature of  the  mix  should  be  frequently  taken  and  recorded 
by  the  Inspector.  In  the  case  of  sheet  asphalt  mixtures  a 
pat  test  (§  380)  should,  in  addition,  be  made  from  time  to 
time  as  a  check  on  proper  proportions.  Daily  samples  of 
the  mix  should  also  be  taken  and  forwarded  to  the  labora- 
tory for  check  on  proportions  and  grading.  The  condition 
and  behavior  of  the  mix  on  the  road,  during  spreading  and 
compaction,  will  often  indicate  the  necessity  for  slight 
modifications  in  proportions  and  temperature,  which  can- 
not be  told  by  inspecting  the  mix  at  the  plant.  For  this 
reason  the  plant  Inspector  should  cooperate  to  the  fullest 
extent  with  the  street  Inspector. 

251.  Output  of  the  Plant.     The  rated  batch  capacity  of 
a  mixer  given  in  cubic  feet  will  not  hold  good  for  all  types 
of  mixes,  but,  for  a  given  job  with  known  batch  weights, 
the  yardage  of  pavement  which  should  be  laid  by  each  load 
is  soon  ascertained,  provided  the  number  of  batches  to  the 
load  is  kept  constant.     The  plant  Inspector  should,  there- 
fore, keep  a  daily  record  of  the  number  of  loads  produced 
and  thus  check  the  yardage  of  pavement  laid  as  measured 
by  the  street  Inspector.    As  described  under  the  individual 
types  of  pavement  (§  262)  it  is  quite  nossible  to  calculate, 
with  reasonable  accuracy,  the  number  of  square  yards  which 
a  load  should  lay  or,  in  other  words,  the  weight  per  square 
yard  of  pavement  of  a  specified  thickness. 

252.  Cooperation   of  Inspectors.     It   is   quite   necessary 
that  the  plant  Inspector  should    cooperate  to   the   fullest 
extent  with  the  street  Inspector,  the  Laboratory  and  the 
Contractor.    The  way  the  mix  handles  on  the  street  is  often 
an  important  guide  to  desirable  modifications  which  may  be 


210     Bituminous  Paving  Plant  Inspection 

made,  within  specification  limits,  in  heating  and  propor- 
tioning the  mix.  If  possible,  the  plant  Inspector  should 
occasionally  visit  the  street  to  observe  conditions  but 
whether  or  not  this  is  done,  he  should  always  keep  in  touch 
with  the  street  Inspector.  The  one  will,  therefore,  serve 
as  a  guide  and  check  to  the  other.  In  like  manner  the  plant 
Inspector  should  submit  suitable  samples  of  the  constitu- 
ents and  of  the  mix  proper  to  the  Laboratory  for  check  and 
control  tests  on  plant  operation.  While  material  violations 
of  specification  requirements  for  plant  operation  and  out- 
put will  warrant  rejection  of  the  mix,  the  Inspector  should 
bear  in  mind  the  fact  that  economical  operation  of  the  pav- 
ing gang  is  dependent  upon  the  rate  of  supply  and  amount 
of  mix  delivered  by  the  plant.  If,  therefore,  slight  varia- 
tions from  specifications  occur  which  make  the  matter  of 
rejection  of  doubtful  necessity,  the  proper  correction  should 
be  made  at  once,  but  the  mix  already  turned  out  may  be 
allowed  to  be  laid  with  the  understanding  that,  if  later  con- 
sidered unsatisfactory  by  the  Engineer,  it  shall  be  removed 
and  replaced  at  the  expense  of  the  Contractor.  In  such 
cases  the  exact  location  of  the  doubtful  mix  in  the  pavement 
should  be  ascertained  and  recorded. 

f)£fr  oi  w?«t'jitt<f -lo . -'iscluuMi 'odi.Jisbr/otq-  .bofii&tteoaii  noo>  '->.[' 
INSPECTOR'S  EQUIPMENT 

253.  The  Plant  Laboratory.  At  the  paving  plant  a  small 
room  should  be  assigned  the  Inspector  for  conducting  neces- 
sary control  tests.  This  room  should  contain  a  stout  work 
bench  for  testing  apparatus,  shelves  for  samples  and  con- 
tainers, a  chair  and  table.  The  exact  testing  equipment 
which  may  be  needed  will  depend  somewhat  upon  the  type 
of  mix  which  is  to  be  produced,  as  indicated  in  the  following 

rflfU- 

For  Sampling, 

A  supply  of  close-woven  bags  for  shipping  samples  of 
aggregate  to  the  laboratory. 


Inspector's  Equipment  211 

A  ball  of  stout  twine. 

A  supply  of  eyelet  tags  for  identification  information. 

A  long-handled  metal  dipper. 

A  supply  of  1 -quart  tin  cans. 

A  supply  of  3-oz.  round  tin  boxes. 

A  supply  of  gum  labels. 

For  Testing: 

A  set  of  standard  screens  and  sieves  as  may  be  called 

for  in  specification  requirements  (§371). 
A  stiff  brush  for  cleaning  sieves. 
A  spring  balance  with  pan  capacity  of  10  pounds  (§  371) 

for  screen  analysis  of  coarse  aggregates  if  used,  or  a 

beam  balance  of  similar  capacity  and  set  of  decimal 

weights. 
A  spring  balance  with  pan  capacity  of  200  grams  (§371) 

for  screen  analysis  of  fine  aggregates,  if  used,  or  a 

sand  scale  of  similar  capacity. 
A  complete  penetration  test  outfit  (§  378)  if  asphalt 

cement  is  used. 

A  complete  float  test  outfit  (§  379)  if  refined  tar  is  used. 
A  complete  pat  test  outfit  (§  380)  if  sheet  asphalt  mix 

is  used. 

A  small  pocket  magnifying  glass. 
A  hand  sample  of  approved  rock  for  visual  comparison 

if  broken  stone  is  used. 

For  Records  and  Reports: 

A  scratch  pad  and  pencil. 

A  supply  of  report  forms  (§  395). 

A  carbon  paper  for  duplication  of  reports. 

254.  Personal  Equipment.    The  Inspector  should  carry 
with  him  for  general  use  the  following  articles: 

A  pocket  rule  (§387). 

An  armored  thermometer  (§  386). 

A  diary  and  pencil. 


CHAPTER  XIII 

INSPECTION  OF  BITUMINOUS  CONCRETE 
AND   SHEET  ASPHALT  PAVEMENTS 

GENERAL  CHARACTERISTICS 

255.  Types  of  Pavement.  Bituminous  concrete  and  sheet 
asphalt  pavements  are  composed  of  a  mixture  of  mineral 
aggregate  and  bituminous  material  prepared  as  a  paving 
composition  and  laid  as  such  upon  a  suitable  foundation. 
They  may  conveniently  be  considered  under  the  following 
seven  classes: 

I.  One-size  stone  bituminous  concrete,  in  which  the 
mineral  aggregate  consists  of  a  single  commercial  size 
of  crushes  product  with  no  exact  grading  limitations. 
II.  Coarse-graded  aggregate  bituminous  concrete,  in  which 
the  mineral  matter  consists  of  a  combination  of  coarse 
and  fine  aggregates  so  proportioned  that  the  former 

predominates  and  the  latter  serves  mainly  as  a  void 
£,,.  ,. 

filling  medium. 

III.  Fine-graded  aggregate  bituminous  concrete,  in  which 
small  size  broken  stone  is  mixed  with  sand  in  such 
proportions  that  the  fine  aggregate  greatly  predomi- 
nates and  thus  separates  the  coarser  stone  fragments 
from  intimate  contact  with  one  another. 

IV.  Asphalt  block,  in  which  a  fine,  carefully  proportioned 
and  graded  bituminous  concrete  is  molded  under  pres- 
sure into  blocks.    This  type  is  considered  under  brick 
and  block  pavements  (§315). 

V.   Sheet  asphalt,  which  consists  of  a  carefully  propor- 
tioned  mixture   of   graded   sand,    mineral   filler   and 
212 


Details  of  Construction  of  all  Types       213 

asphalt  cement,  thus  producing  a  dense  homogeneous 
mortar. 

VI.  A  natural  bituminous  sandstone  or  bituminous  lime- 
stone suitably  prepared  for  spreading  as  a  bituminous 
mortar  or  mastic.  The  characteristics  of  the  former 
variety  are  similar  to  sheet  asphalt,  while  those  of  the 
latter  more  nearly  approach  the  bituminous  earth 
type. 

VII.  Bituminous  earth  in  which  the  mineral  aggregate  con- 
sists of  finely  divided  soil,  such  as  clay,  with  no  well 
defined  grading  limitations. 

256.  General  Method  of  Construction.    The  bituminous 
mixture,  ordinarily  prepared  at  a  paving  plant,  is  evenly 
spread  upon  the  foundation  so  as  to  produce  after  compac- 
tion a  wearing  course  of  the  desired  thickness,  usually  about 
2  inches.    With  the  exception  of  certain  rock  asphalt  prepa- 
rations   and   mixtures,  containing    cut-back   or    emulsified 
asphalt  or  cut-back  refined  tar,  the  mixture  is  laid  and  rolled 
while  still  hot  from  the  paving  plant.     On  bituminous  con- 
crete which  after  compaction  shows  a  surface  of  open  tex- 
ture the  pavement  may  be  given  a  seal  coat  of  hot  bitumi- 
nous material,  followed  by  a  light  covering  of  stone  chips  or 
sand  which  is  forced  into  the  surface  voids  by  rolling.     If 
the  surface  is  of  close  texture  the  pavement  is  often  finished 
off  with  a  dusting  of  mineral  filler.     In  the  fine  aggregate 
and  sheet  types  of  pavement,  what  is  known  as  a  binder 
course  of  bituminous  concrete  may  be  interposed  between 
the  foundation  and  pavement  proper 

DETAILS   OF  CONSTRUCTION  APPLICABLE  TO 
ALL  TYPES 

257.  Foundations.     Bituminous   concrete   and   sheet   as- 
phalt pavements  are  commonly  laid  on  a  cement  concrete 
foundation,  the  surface  of  which  is  slightly  rough  (§219a). 
They  are    sometimes    laid    upon    a    bituminous    concrete 


214    Bituminous  Concrete  and  Sheet  Asphalt 

foundation  and  sometimes  upon  an  old  gravel  or  ma- 
cadam road  which  is  first  prepared  by  patching  (§  1736) 
or  resurfacing  (§  173c).  Unless  resurfacing  is  absolutely 
necessary,  due  to  lack  of  thickness,  such  foundations  should 
be  disturbed  as  little  as  possible  and  the  introduction  of  a 
binder  course  is,  therefore,  sometimes  adopted  for  the  pur- 
pose of  truing  up  the  surface  to  receive  the  pavement 
proper.  The  same  is  true  when  old  Telford,  cobble  stone 
block,  brick  or  cement  concrete  pavements  are  utilized  as 
foundations.  In  general,  irregularities  in  thickness  of 
binder  or  wearing  courses  are  to  be  avoided,  however,  so 
that  in  new  concrete  foundation  construction  it  is  important 
that  the  surface  be  true  and  carry  the  same  crown  as  the 
finished  pavement.  Sometimes  a  thin  paint  coat  of  cut- 
back bituminous  cement  is  applied  to  the  carefully  cleaned 
surface  of  the  concrete  foundation  for  the  purpose  of  bond- 
ing the  pavement  to  the  foundation. 

258.  Preparation  of  the  Bituminous  Aggregate,  (a)  The 
bituminous  aggregate  is  usually  prepared  at  a  paving  plant 
from  which  it  is  delivered  on  the  job  by  wagons,  carts  or 
trucks.  Hand  mixing,  with  preheated  aggregate  and  bitu- 
minous cement,  is  possible  for  the  large  aggregate  concretes 
but  neither  as  satisfactory  nor  economical  as  properly  con- 
ducted mechanical  mixing.  In  place  of  the  regular  paving 
plant,  for  the  cheaper  types  of  construction,  more  or  less 
successful  attempts  have  been  made  to  utilize  the  batch 
type  of  concrete  mixer,  in  which  the  aggregate  is  sometimes 
heated  by  means  of  a  large  gasoline  torch  before  the  bitu- 
minous material  is  introduced.  Accurate  control  of  tempera- 
ture and  proportions  is,  however,  difficult  to  secure  unless 
the  mixing  operation  is  conducted  at  a  paving  plant  proper 
(§237).  The  same  factors  which  govern  paving  plant 
inspection,  of  course,  apply  to  the  preparation  of  the  mix 
by  the  methods  above  described,  and  inspection  of  such 
work  should  approach  as  closely  as  practicable  that  of 
paving  plant  inspection. 


Details  of  Construction  of  all  Types     215 

(6)  For  some  types  of  work  cut-back  bituminous  cements 
or  emulsified  asphalts  are  mixed  with  unheated  mineral 
aggregate  either  by  hand  or  in  ordinary  concrete  mixers. 
Such  bituminous  concrete  is,  however,  more  commonly  used 
for  patching  than  for  straight  construction. 

259.  Function  and  Characteristics  of  Mineral  Filler. 
(a)  Many  specifications  for  bituminous  concrete,  and  prac- 
tically all  specifications  for  sheet  asphalt,  require  the  addi- 
tion of  mineral  filler  to  the  mix  during  preparation.  While 
a  great  many  finely  divided  mineral  substances  have  been 
utilized  as  filler,  those  most  commonly  specified  and  used  are 
limestone  dust  and  Portland  cement.  These  products  have, 
in  general,  been  found  most  satisfactory  because  of  their 
availability,  the  ease  with  which  they  may  be  combined 
in  the  mix  without  balling  up,  their  extreme  fineness  and 
the  toughening  effect  which  they  produce  upon  the  mix. 
Specifications  for  fineness  of  limestone  dust,  including  also 
dolomite  dust  (§  199),  usually  require  100  per  cent  to  pass 
the  30-mesh  sieve  and  at  least  66  per  cent  to  pass  the  200- 
mesh  sieve.  The  same  requirements  are  made  for  Portland 
cement  filler  although  this  material  under  the  standard 
specifications  will  show  at  least  78  per  cent  passing  the 
200-mesh  sieve.  All  mineral  filler  should,  of  course,  be 
perfectly  dry  when  used. 

-(6)  The  voids  in  loose  dry  filler  vary  greatly  according 
to  the  type  of  filler,  its  degree  of  fineness  and  method  of 
handling.  Consequently,  a  given  weight  does  not  repre- 
sent a  constant  loose  volume.  In  proportioning  it  is,  there- 
fore, preferable  to  measure  filler  by  weight  rather  than  by 
volume  in  order  to  secure  a  uniform  mix.  It  should  not  be 
forgotten,  however,  that  one  of  the  objects  of  using  a  filler 
is  to  fill  voids,  so  that  the  volume  of  space  occupied  by  the 
filler  is  of  considerable  importance.  When  present  in  a 
compacted  mix,  both  limestone  dust  and  Portland  cement 
filler  may  be  assumed  to  contain  40  per  cent  voids.  As  they 
are  equivalent  in  this  respect,  equivalent  volumes  will  be 


216     Bituminous  Concrete  and  Sheet  Asphalt 

represented  by  different  weights  and  percentages  of  the  mix, 
depending  upon  their  difference  in  specific  gravity.  This 
fact  should  be  borne  in  mind  when  proportioning  by  weight. 
Thus,  the  specific  gravity  of  Portland  cement  is  3.1  while 
that  of  limestone  is  about  2.7.  Therefore,  in  a  mix  2.7 
pounds  of  limestone  dust  is  equal  to  3.1  pounds  of  Portland 
cement  as  a  void  filler.  One  pound  of  limestone  dust  is 
equal  to  1.15  pounds  Portland  cement  and  one  pound  of 
Portland  cement  is  equal  to  0.87  pound  of  limestone  dust. 
260.  Spreading  the  Bituminous  Aggregate,  (a)  Bitumi- 
nous aggregates  delivered  from  the  mixing  plant  should 
arrive  on  the  road  at  such  temperature  that  they  may  be 
readily  spread  and  compacted.  The  temperature  of  the 
loads  as  received  should,  therefore,  be  frequently  ascer- 
tained by  the  Inspector.  Before  placing  the  mix,  the  founda- 
tion should  be  thoroughly  clean  and  dry.  Loads  should 
never  be  dumped  in  place  but  should  be  shoveled  from  piles 
preferably  deposited  upon  a  dumping  board.  Each  pile 
should  be  shoveled  from  the  bottom  and  the  mix  deposited 
on  the  road  by  turning  the  shovel  completely  over.  It  is 
then  spread  by  means  of  hot  rakes  to  such  thickness  as, 
after  compaction,  will  produce  the  specified  thickness  of 
pavement.  The  rakers  should  not  stand  on  the  hot  mix 
more  than  absolutely  necessary.  When  raking  coarse 
graded  bituminous  aggregates,  the  largest  fragments  may 
tend  to  come  to  the  top  and  if  this  tendency  becomes  too 
pronounced,  accumulations  of  such  fragments  should  be 
raked  in  advance  of  the  layer  so  as  to  be  completely  covered 
when  spreading  the  next  load.  All  contact  surfaces  of  curbs, 
gutters,  manholes,  etc.,  should  be  lightly  but  uniformly 
painted  with  hot  bituminous  cement  in  order  to  bond  them 
to  the  mix.  Measurement  of  loose  and  compacted  depth 
of  the  hot  mix  may  be  made  with  a  screw  driver  or  stiff 
putty  knife.  The  exact  relation  between  loose  and  com- 
pacted thickness  cannot  be  accurately  foretold  for  any  type 
of  mix  as  this  will  depend  upon  the  extent  to  which  the  par- 


Details  of  Construction  of  all  Types      217 

ticular  mix  fluffs  up  or  settles  during  spreading.  Control 
of  thickness  is  better  secured  by  ascertaining  the  yardage 
that  each  load  of  known  weight  should  lay  and  measuring 
off  the  proper  distance  for  each  load  on  the  curb  or  edging. 
This  is  determined  from  the  weight  per  square  yard  of  com- 
pacted pavement  (Figs.  27  to  34).  Depth  of  mix  at  the 
sides  may  be  measured  directly  on  the  curbs,  gutters  or  edg- 
ing. Side  protection  by  such  forms  of  construction  is  highly 
desirable  but  sometimes  the  mix  is  laid  and  compacted  be- 
tween plank  runners  of  suitable  thickness  laid  along  the 
sides  of  the  road.  After  completion  of  the  pavement  proper, 
these  runners  may  be  moved  to  an  advanced  position  and 
the  bituminous  aggregate  protected  by  the  construction  of 
well-consolidated  broken  stone  or  gravel  shoulders. 

(6)  As  the  behavior  of  the  mix  during  construction  will 
often  indicate  desirable  modifications  in  its  preparation  at 
the  plant,  the  street  Inspector  should  keep  in  close  com- 
munication with  the  plant  Inspector  and  advise  him  of  the 
temperature  at  which  the  mix  is  received  on  the  road, 
whether  it  appears  to  be  too  sloppy  or  too  dry,  whether  or 
not  it  is  too  stiff  to  rake  properly,  or  tends  to  ball  up,  and 
how  the  surface  closes  up  under  compaction.  Specifications 
frequently  contain  a  clause  relative  to  the  minimum  air 
temperature  at  which  the  pavement  may  be  laid.  In  cold 
weather,  therefore,  the  Inspector  should  record  air  tempera- 
tures during  progress  of  the  work. 

261.  Compacting  and  Finishing.  Bituminous  aggregates 
should  be  compacted  by  rolling,  while  hot,  and  as  soon  as 
possible  after  spreading  and  raking.  If  allowed  to  cool  or  set 
up  before  rolling,  satisfactory  compaction  cannot  be  ob- 
tained, While  the  ordinary  three-wheel  road  roller  is  some- 
times used  for  coarse  aggregates,  the  use  of  tandem  rollers 
is  to  be  preferred  for  fine  aggregates.  Initial  compaction  is 
sometimes  secured  by  the  use  of  a  roller  of  light  weight  and 
final  compaction  with  a  heavier  roller,  usually  from  7  to  8 
tons  in  weight.  If  the  mix  tends  to  adhere  to  the  wheels  of 


218    Bituminous  Concrete  and  Sheet  Asphalt 

the  roller  they  should  be  mopped  with  kerosene  and  water 
during  the  rolling  operation.  Rolling  should  commence  at 
one  side  parallel  to  the  curb  or  edging  and  each  trip  of  the 
roller  should  overlap  the  preceding  one  until  the  center 
line  of  the  road  is  reached,  when  the  operation  is  repeated, 
starting  at  the  other  side.  The  roller  should  proceed  slowly 
and  alternate  trips  should  be  of  slightly  different  length  to 
prevent  wave  deformation  of  the  surface.  If  the  pavement 
is  of  sufficient  width,  the  second  rolling  is  made  diagonally 
across  the  center  line  and  later  followed  by  cross  rolling. 
Places  which  cannot  be  reached  with  a  roller  should  be 
compacted  and  finished  with  hot  tampers  and  smoothers. 
Unless  a  coarse  aggregate  is  being  laid  as  wearing  course, 
to  be  followed  with  a  seal  coat,  or  as  binder  course,  the  sur- 
face of  a  well-proportioned  mix  should  close  up -under  roll- 
ing. Spots  which  do  not  close  up  may  require  finishing  with 
hot  smoothing  irons,  but  great  care  should  be  exercised 
that  the  mixture  is  not  burned  by  such  treatment,  or  scal- 
ing of  the  surface  under  traffic  will  result. 

(b)  Rolling  should  be  conducted  as  continuously  as  possi- 
ble to  avoid  the  formation  of  numerous  joints.  When  the 
operation  is  temporarily  discontinued,  as  at  the  end  of  a 
day's  work,  the  last  load  may  be  rolled  to  a  featheredge  in 
which  case,  when  work  is  resumed,  the  mix  should  be  cut 
back  so  as  to  produce  a  slightly  beveled  edge  for  the  full 
thickness  of  pavement.  The  material  which  has  been  cut 
back  should  then  be  removed  from  the  work  and  new  mix 
laid  against  the  fresh  cut.  A  better  method  of  forming 
joints  consists  of  rolling  into  the  hot  mix  a  stout  rope  which 
is  laid  across  the  pavement  close  to  the  finishing  edge.  This 
rope  is  allowed  to  remain  in  place  until  work  is  resumed 
when  it  is  removed,  together  with  all  surplus  material  on 
the  far  side,  and  fresh  mix  is  then  laid  against  the  joint 
thus  formed.  Sometimes  the  edge  of  a  joint  is  painted  with 
hot  bituminous  cement  but  this  practice  is  apt  to  lead  to  the 
formation  of  an  undesirable  fat  streak  across  the  pavement. 


Details  of  Construction  of  all  Types      219 

(c)  After  final  compaction  the  surface  of  a  close  mix 
pavement  is  usually  finished  by  a  sweeping  with  limestone 
dust  or  Portland  cement.  An  intermediate  or  binder  course 
(§  278)  is  purposely  left  with  a  slightly  open  surface  and 
should  be  clean  and  free  from  dust  or  dirt  when  the  pave- 
ment proper  is  laid  upon  it.  Coarse  aggregate  bituminous 
concrete  pavements,  as  a  rule,  have  a  somewhat  open  sur- 
face and  are  usually  completed  with  a  surface  treatment  or 
seal  coat  of  bituminous  cement  applied  and  covered  the 
same  as  in  bituminuous  macadam  construction  (§  198). 
Hand  pouring,  or  small  mechanical  distributors,  are  used 
for  this  purpose  together  with  a  squeegee.  Sometimes  the 
surface  voids  are  filled  with  a  very  light  application  of  a 
bituminous  sand  mixture,  prepared  at  the  paving  plant,  in- 
stead of  with  the  ordinary  seal  coat.  In  such  cases  the 
bituminous  sand  aggregate  while  hot  is  spread  over  the  sur- 
face and  rolled  in  so  as  to  produce  a  layer  of  not  over  J  inch 
in  thickness. 

262.  Measurement.  Bituminous  concrete  and  sheet  as- 
phalt pavements  are  commonly  paid  for  upon  a  square  yard 
basis  complete  in  place.  The  Inspector  should,  therefore, 
make  measurements  of  length,  width  and  depth  and  in  addi- 
tion record  the  number  of  loads  or  weight  of  mix  used,  as  a 
check  upon  such  measurements.  Thus,  if  the  weight  per 
load  is  known  as  well  as  the  weight  per  square  yard  of  pave- 
ment, the  length  of  pavement  which  each  load  should  lay 
is  ascertained  from  the  following  formula.  In  this  formula 
x  equals  length  in  inches  which  should  be  laid  by  one  load, 
a  equals  width  of  pavement  in  feet,  b  equals  weight  of  load 
and  c  equals  weight  of  pavement  per  square  yard. 

=  1086T 
ac 

If  x  equals  the  length  in  feet  instead  of  inches,  then 

96 


220     Bituminous  Concrete  and  Sheet  Asphalt 

Sometimes  the  bituminous  cement  is  paid  for  as  a  separate 
item  but,  except  for  paint  coat  and  seal  coat  work,  the  plant 
Inspector  should  ascertain  the  amount  used  from  his  inspec- 
tion of  the  mix.  Measurements  by  volume  or  weight  of 
materials  used  in  seal  coat  work  should  be  made  as  a  check 
upon  the  added  thickness  of  pavement  due  to  such  seal 
coat  as  in  the  case  of  bituminous  macadam  (§  204).  Under 
the  various  types  of  pavements  in  the  following  paragraphs 
diagrams  are  shown  which  may  be  of  service  to  both  plant 
and  street  Inspectors,  in  connection  with  the  measurement 
of  materials  in  the  mix  proper. 

263.  Sampling.     Samples  of  the  constituents  of  the  mix, 
and  also  of  the  product  turned  out  by  the  mixer,  are  taken 
by  the  plant  Inspector.     Occasional  check  samples  of  the 
mix  as  received  upon  the  work  should  be  taken  by  the 
street  Inspector  and  forwarded  to  the  laboratory.    In  addi- 
tion, it  is  highly  desirable  to  take  samples  of  the  finished 
pavement  both  for  laboratory  analysis  as  to  proportions 
and  for  density  determinations.     Such  a  sample  measuring 
about  one  foot  square  should  be  carefully  cut  with  an  ax 
from  each   10,000  square  yards,   and  fractional  area  over 
this   amount    of   pavement,    extending   through   its   entire 
depth   before   any   seal   coat   is   applied.     The   compacted 
depth  is  measured  at  the  point  from  which  the  sample  is 
removed   and  the  exact  location  recorded.     Each   sample 
should  be  very  carefully  packed  for  shipment  to  the  labora- 
tory so  that  it  will  be  received  intact.     Cover  for  seal  coat 
should  be  sampled  and  tested  exactly  as  for  bituminous 
macadam  work  (§205).     A  sample  of  asphalt  for  paint  or 
seal  coat  should  be  taken  from  each  shipment  received  on 
the  work. 

'"    v1'*        '•  ••'    ' 

ONE-SIZE  STONE  BITUMINOUS  CONCRETE 

264.  The    Mineral    Aggregate.     The    mineral    aggregate 
for  one-size  stone  bituminous  concrete  consists  of   a  single 


One-size  Stone  Bituminous  Concrete      221 

size  of  crusher  product,  carrying  little  or  no  fine  aggregate 
and  with  no  exact  grading  limitations.  It,  therefore,  pro- 
duces what  is  commonly  known  as  an  open  mix,  which  re- 
quires a  seal  coat.  The  rock  itself  should  possess  the  same 
general  characteristics  as  for  bituminous  macadam  con- 
struction (§  199a)  although  reasonably  high  toughness  is  of 
greater  importance  owing  to  the  fact  that  little  excess  bitu- 
men is  present,  in  the  pavement,  to  bond  and  hold  in  place 
fragments  which  may  be  fractured  by  the  impact  of  traffic. 
Typical  specifications  of  the  U.  S.  Bureau  of  Public  Roads 
require  a  minimum  French  coefficient  (§  28)  of  wear  of  8 
and  a  minimum  toughness  (§  29)  of  8  for  the  rock.  The 
size  or  grading  required  in  these  specifications  is  as  follows: 

Aggregate  Per  cent 

Passing  1-inch  screen,  not  less  than 95 

Total  passing  f -inch  screen 25-75 

Retained  on  J-inch  screen,  not  less  than . .        85 

Chips  for  Seal  Coat 

Passing  J-inch  screen,  not  less  than 95 

Retained  on  J-inch  screen,  not  less  than .  .        85 

265.  The  Bituminous  Material.  Asphalt  cements  (§  96) 
or  refined  tars  (§  103)  are  used  as  binders  for  this  type  of 
construction.  For  each  class  of  material  the  same  con- 
sistency of  product  is  used  for  both  mix  and  seal  coat.  Some- 
times, however,  asphalt  cement  is  used  for  seal  coat  when 
tar  is  used  in  the  mix.  As  in  bituminous  macadam  con- 
struction the  most  desirable  consistency  of  bituminous 
cement  will  depend  mainly  upon  climatic  conditions  but 
may  also  be  influenced  by  traffic  and  the  quality  of  stone 
used.  In  general,  somewhat  harder  cements  are  used  than 
for  bituminous  macadam,  subjected  to  the  same  climatic 
conditions,  as  illustrated  by  the  following  requirements  of  typ- 
ical specifications  of  the  U.  S.  Bureau  of  Public  Roads.  Fluxed 
native  asphalts,  containing  more  than  6  or  7  per  cent 
of  nonbituminous  material  (§§  96c,  133)  are  seldom  used 


222     Bituminous  Concrete  and  Sheet  Asphalt 

in  this  type  of  work  but  refined  tars  may  contain  as  high 
as  20  per  cent  or  more  of  free  carbon  (§  102c).  The  per- 
centage of  total  bitumen  as  well  as  the  specific  gravity 
of  the  bituminous  material  are,  of  course,  important  con- 
siderations to  the  plant  Inspector,  when  proportioning  a 
mix  upon  a  weight  basis  although  for  this  type  of  pavement 
the  presence  of  as  high  as  5  per  cent  of  impurities  may 
usually  be  ignored.  Various  other  characteristics  commonly 
specified  are  shown  under  Typical  Material  Requirements 
(§§411,  412). 


Asphalt  Cement 

Refined  Tar 

General  Climatic  Conditions 

Penetration 
@  25°  C. 

Float  Test 
©  50°  C. 

Northern  U  S 

80-90 

120-150  seconds 

Southern  US 

70-80 

150-180  seconds 

266.  The  Mix.  (a)  Specification  limits  for  the  propor- 
tion of  constituents  in  the  mix  usually  require  from  18  to 
21  gallons  of  bituminous  material  per  cubic  yard  of  broken 
stone  or  on  a  weight  basis  from  5  to  7  or  8  per  cent  of  bitu- 
men in  the  mix.  For  an  aggregate  coming  within 'the  typical 
limits  of  grading  (§  264)  approximately  19.8  gallons  per 
cubic  yard  will  be  required.  Voids  if  measured  by  volume 
in  the  loose  stone  may  be  assumed  at  45  per  cent  and  in 
the  compacted  stone  as  30  per  cent  without  figuring  in  the 
space  occupied  by  the  bitumen.  Upon  this  basis  Fig.  27 
shows  the  number  of  pounds  of  constituents  per  square  yard 
of  compacted  mix  2  inches  thick,  which  is  the  depth  ordi- 
narily laid.  If  the  surface  of  the  foundation  is  not  rigid  or 
is  uneven,  somewhat  greater  quantities  will  be  required. 
The  effect  of  variations  in  specific  gravity  of  the  constituents 
of  the  mix  upon  the  weight  of  pavement  per  square  yard  is 
clearly  shown  in  these  diagrams,  as  well  as  the  effect  of 
impurities  on  the  amount  of  bituminous  material  required. 


One-size  Stone  Bituminous  Concrete       223 

(6)  This  diagram  is  not  only  useful  as  a  guide  to  propor- 
tioning the  mix  by  weight  but  also  in  determining  the  length 
of  pavement  that  should  be  laid  by  each  load  of  known 
weight.  Thus,  if  the  specific  gravity  of  the  rock  is  2.7  and 

SPECIFIC  GRAVITY  OF  ROCK 
2.4  2,6  2.8  3.0 


1.0  1.1  1.2  1.3 

SPECIFIC  GRAVITY  OF  BITUMINOUS  MATERIAL 


10 


Fig.  27 


Quantities  of  Materials  Required  for  Construction 
of  One-size  Stone  Bituminous  Concrete 


that  of  the  bituminous  material  1.05  with  no  impurities 
present,  it  is  ascertained  from  the  diagram  that  175.4  pounds 
of  rock  and  12.1  pounds  of  bituminous  material  should  be 
present  in  each  square  yard  of  pavement.  The  total  weight 
of  pavement  per  square  yard  is,  therefore,  187.5  pounds. 


224   .Bituminous  Concrete  and  Sheet  Asphalt 

This  weight  may  be  used  in  the  formula  given  under  meas- 
urements (§  162)  for  determining  the  length  of  pavement 
which  should  be  laid  with  each  load  of  known  weight. 

(c)  If  proportions  are  measured  by  volume  only  then  the 
length  of  pavement  which  should  be  laid  per  load  may  be 
ascertained  from  the  following  formula  in  which  x  equals 
the  length  in  inches  which  should  be  laid  for  one  load,  a 
equals  width  of  pavement  in  feet,  b  equals  cubic  feet  of 
loose  stone  per  batch,  and  c  equals  the  number  of  batches 
to  a  load. 


If  x  represents  the  length  in  feet  instead  of  inches,  then 

hr 

3-4.8X-- 

a 

(d)  The  variation  in  weight  proportions  for  the  same 
volume  proportions  in  the  mix  may  be  illustrated  by  a  com- 
parison of  two  mixes  as  follows: 

Mix  A  composed  of  asphalt  of  1.02  specific  gravity  contain- 
ing 100  per  cent  bitumen  and  rock  of  3.0  specific  gravity. 

Mix  B  composed  of  tar  of  1.25  specific  gravity  containing 
80  per  cent  bitumen,  and  rock  of  2.6  specific  gravity. 

From  the  diagram  the  weight  of  constituents  per  square 
yard  for  each  mix  is  ascertained  and  the  percentage  by 
weight  for  each  constituent  calculated. 


Mix  A 

MixB 

Weight 

Per  cent 

Weight 

Per  cent 

Bituminous  Material  
Broken  Stone 

11.7  = 
194.5  = 

5.7 
94.3 

17.8  = 
169.0  = 

9.5 
90.5 

206.2 

100.0 

186.8 

100.0 

While  mix  B  contains  9.5  per  cent  of  bituminous  material 
this  figure  should  be  multiplied  by  0.8  to  ascertain  the  actual 


Coarse  Graded  Bituminous  Concrete      225 

amount  of  bitumen  present.  When  this  is  done  mix  B  is 
found  to  contain  7.6  per  cent  bitumen  by  weight  while  mix 
A  contains  5.7  per  cent.  There  is,  therefore,  a  difference  of 
over  2  per  cent  by  weight  although  the  volume  proportions 
are  the  same. 

(e)  Voids  in  the  compacted  mix  exclusive  of  the  seal  coat 
as  determined  from  the  density  of  the  pavement  (§  384) 
should  closely  approach  the  voids  calculated  as  follows. 
Assuming  the  voids  in  the  compacted  stone  as  30  per  cent, 
the  volume  of  voids  per  square  yard  two  inches  thick  is, 
(36  x  36  x  2  inches)  x  0.3  =  777.6  cubic  inches.  If  1.38 
gallons  of  bitumen  per  square  yard  is  present  in  the  mix  the 
volume  which  it  occupies  is  231  cubic  inches  x  1.38  =  318.8 
cubic  inches.  Subtracting  this  volume  from  the  volume  of 
voids  gives  777.6  -  318.8  =  458.8  cubic  inches  of  voids  per 
square  yard  of  pavement.  As  a  square  yard  2  inches  thick 
amounts  to  2592  cubic  inches,  the  calculated  percentage  of 

voids  is 

100  x  458.8 


2592 


=  17.7  per  cent. 


267.  The  Seal  Coat.     The  quantities  of  materials  used 
for  seal  coating  this  type  of  pavement  are  about  the  same 
as  for  bituminous  macadam  (Fig.  23).     Approximately  0.4 
gallon  of  bituminous  material  and  0.02  cubic  yard  of  cover 
will  be  required  for  each  square  yard  of  mix  laid.     The 
bituminous  material  should  preferably  be  squeegeed  over 
the  surface. 

COARSE  GRADED  AGGREGATE  BITUMINOUS 
CONCRETE 

268.  The  Coarse  Aggregate.     The  coarse  aggregate  for 
this  type  of  pavement  may  consist  of  broken  stone,  broken 
slag   or  gravel.     If  of  broken  stone,  it  should  possess  the 
same  physical  characteristics  as  given  for  the  preceding  type 
of  pavement  (§264).     Typical  specifications  of  the  U.  S. 


226     Bituminous  Concrete  and  Sheet  Asphalt 

Bureau  of  Public  Roads  call  for  a  French  coefficient  of  wear 
of  not  less  than  8  and  a  toughness  of  not  less  than  8.  The 
same  French  coefficient  may  be  specified  for  slag  together 
with  a  maximum  weight  per  cubic  foot  of  not  less  than  65 
pounds.  It  is  particularly  important  that  gravel,  if  used, 
be  composed  of  sound  durable  pebbles  and  it  should  be  care- 
fully inspected  from  this  standpoint  by  means  of  the  hammer 
test  (§  374) .  Cover  for  seal  coat  is  generally  of  the  same 
type  of  material  as  coarse  aggregate.  Sometimes  a  bitu- 
minous sand  mix  seal  coat  is  used,  however,  in  which  case 
the  fine  aggregate  (§  269)  is  used.  Typical  specification  of 
the  U.  S.  Bureau  of  Public  Roads  for  grading  of  the  coarse 
aggregate  and  seal  coat  cover  are  as  follows: 

Coarse  Aggregate  Per  cent 

Passing  1-inch  screen,  not  less  than.  .  ., , . .;  j  95 
Total  passing  f-inch  screen.  .;U.  .^f,,..  yv'^  25-75 
Retained  on  J-inch  screen,  not  less  than .  .  85 

Cover  for  Seal  Coat 

&('{"'  *•' 
Passing  J-inch  screen,  not  less  than 95 

Retained  on  J-inch  screen,  not  less  than .  .        85 

269.  Fine  Aggregate.  The  fine  aggregate  should  pref- 
erably consist  of  hard,  sharp,  uncoated  quartz  sand  al- 
though a  mixture  of  sand,  and  stone  or  slag  screenings  is 
sometimes  allowed.  No  rigid  grading  requirements  are 
usually  specified  as  dependence  upon  the  stability  of  the 
mix  is  put  upon  the  interlocking  of  the  fragments  of  coarse 
aggregate  which  predominate.  The  fine  aggregate  should, 
however,  be  neither  too  coarse  nor  too  fine.  The  U.  S. 
Bureau  of  Public  Roads  typical  specifications  for  grading 
are  as  follows: 

Per  cent 

Passing  J-inch  screen 100 

Total  passing  40-mesh  sieve 30-70 

'Retained  on  200-mesh  sieve,  not  less  than. . .        90 


Coarse  Graded  Bituminous  Concrete      227 

270.  The  Bituminous  Material.     Asphalt  cements  (§  96) 
are  now  ordinarily  used  as  binders  for  this  type  of  pavement 
although  refined  tars  (§  103)  have  been  used  to  some  extent. 
If  used,  the  characteristics  of  the  tars  should  be  the  same 
as  stated  under  the  one-size  stone  type  of  pavement  (§  265). 
Among  the  asphalt  cements,  those  refined  from  petroleum 
and  also  fluxed  Bermudez  asphalt  are  most  commonly  em- 
ployed.   As  the  amount  of  bitumen,  in  the  former,  approxi- 
mates 100  per  cent,  and,  in  the  latter,  95  to  97  per  cent 
(§§  96c,  133)  there  is  little  need  for  taking  the  non-bitumi- 
nous impurities  into  account  when  such  asphalts  are  used. 
If  refined  tar  or  fluxed  Trinidad  asphalt  are  used,  however, 
allowance  should  be  made  for  non-bituminous  impurities 
in    connection    with    proportioning.      The    most    desirable 
consistency  of  asphalt  cement  is  slightly  harder  than  for 
the   one-size   broken   stone    concrete  under   the  same   cli- 
matic  conditions.      Typical    specifications    of    the    U.    S. 
Bureau   of   Public    Roads   require    a    penetration   of   from 
70   to   80   for   northern   climates   and    from   60   to   70  for 
southern     climates.     Various     other    characteristics    com- 
monly   specified   are   shown  under  Typical    Material    Re- 
quirements (§  411). 

271.  The  Mix.     (a)  The  mix  for  this  type  of  pavement 
may  be  proportioned  in  a  number  of  different  ways  with 
the  idea  of  producing  a  dense  bituminous  concrete,  in  which 
the   coarse   mineral   fragments   are   brought   into   intimate 
contact    and    produce    considerable    mechanical    stability, 
which  is  increased  by  the  presence  of  fine  aggregate  in  filling, 
as  completely  as  possible,  all  interstitial  voids.     Sometimes 
the  entire  aggregate  is  screened  into  various  sizes  which 
are  recombined,  in  such  proportions  as  to  produce  maximum 
density.     It  is,  however,  generally  satisfactory  to  consider 
the  main  aggregate  as  composed  of  only  two  constituents, 
coarse  aggregate  and  fine  aggregate.    Mineral  filler  is  ordi- 
narily added  to  as  great  an  extent  as  the  mix  will  comfort- 
ably carry,  without  interfering  with  its  workability.    Upon 


228     Bituminous  Concrete  and  Sheet  Asphalt 

this  basis  weight  proportions  will  usually  come  within  the 
following  limits : 

Per  cent 

Coarse  aggregate 45-60 

Fine  aggregate 25-40 

Mineral  filler 3-5 

Bitumen 6-8 

-./'••.'••'.'  •':'"'(  V '.  i  •;  _  •     - 

Coarse  aggregates  retained  on  the  J-inch  screen  and  fine 
aggregates  meeting  the  grading  requirements  given  in  the 
preceding  paragraphs  (§§  267-268)  may  be  assumed  to 
contain  40  per  cent  voids  compacted.  In  such  case  40  parts 
by  volume  of  fine  aggregate  will  be  required  to  fill  the  voids 
in  100  parts  of  coarse  aggregate.  The  volume  proportions 
of  coarse  to  fine  would  then  be  1  : 0.4  or  2J  :  1.  While  an 
excess  of  fine  aggregate  i$  undesirable,  unless  very  dense 
in  itself,  more  than  the  theoretical  quantity  is  required  to 
produce  a  close  surface,  owing  to  a  certain  amount  of  un- 
avoidable segregation  during  spreading  and  raking.  The 
most  practical  volume  proportions  will  usually  lie  between 
1.8  and  2  parts  of  coarse  aggregate  to  1  part  of  fine  aggregate. 
Upon  this  basis  and  assuming  the  sand  to  have  a  constant 
specific  gravity  of  2.65,  Fig.  28  shows  the  approximate 
number  of  pounds  of  each  constituent  required  to  produce 
one  square  yard  of  compacted  mix,  with  a  uniform  thickness 
of  2  inches,  taking  into  account  normal  variations  in  specific 
gravity  and  allowing  for  as  high  as  15  per  cent  of  fine  aggre- 
gate in  the  broken  stone  product.  i  dm 

(6)  This  diagram  may  be  used  as  described  for  Fig.  27 
(f  2666)  for  determining  weight  per  square  yard  and  length 
of  pavement  which  should  be  laid  per  load  of  mix  of  known 
weight  (§  162).  If  proportions  are  measured  by  volume  the 
length  of  pavement  which  should  be  laid  per  load  may  be 
ascertained  from  the  following  formula  in  which  x  equals 
length  in  inches  which  should  be  laid  for  one  load,  a  equals 
width  of  pavement  in  feet,  b  equals  cubic  feet  of  loose  stone, 


Coarse  Graded  Bituminous  Concrete      229 


SPECIFIC  GRAVITY  OF  ROCK 
2.4  2.6  2.8  3.0 


15  10  5 

$  FINE  AGGREGATE  IN  STONE 


0.98  1.00  1.02  1.04  1.06 

SPECIFIC  GRAVITY  OF  ASPHALT  CEMENT 

Fig.  28     Quantities  of  Materials  Required  for  Construction  of 
Coarse  Graded  Aggregate  Bituminous  Concrete 

with  45  per  cent  of  voids,  per  batch,  and  c  equals  the  number 
of  batches  to  the  load. 


If  x  represents  the  length  in  feet  instead  of  in  inches  then 


230    Bituminous  Concrete  and  Sheet  Asphalt 

(c)  Voids  in  the  compacted  mix  exclusive  of  seal  coat,  as 
determined  from  the  density  of  the  pavement  (§  384),  should 
be  less  than  3  per  cent. 

272.  The  Seal  Coat.  The  quantities  of  materials  used 
for  seal  coating  this  type  of  pavement  are  usually  less  than 
for  the  one-size  stone  type  (§  267)  as  the  surface,  after  com- 
paction, is  less  open.  From  0.2  to  0.3  gallon  of  bituminous 
material  per  square  yard  may  be  squeegeed  over  the  surface, 
and  cover  amounting  to  0.015  cubic  yard  per  square  yard 
will  usually  prove  sufficient.  Sometimes  a  mixture  of  about 
85  per  cent  of  fine  aggregate,  5  per  cent  mineral  filler  and 
10  per  cent  bitumen  is  prepared  at  the  plant  for  spreading 
over  the  compacted  mix  so  as  to  produce  a  smooth  texture 
surface.  For  each  square  yard  this  will  require  about  22 
pounds  of  sand,  1.3  pounds  of  filler  and  2.6  pounds  of 
bitumen,  and  will  give  an  additional  thickness  of  about 
i  inch. 


FINE  GRADED  AGGREGATE  BITUMINOUS 
CONCRETE;  TOPEKA  TYPE 

273.  The  Broken  Stone  Aggregate.  Broken  stone  for 
this  type  of  pavement  is  intended  primarily  to  supply  the 
mineral  aggregate  with  fragments  passing  the  j-inch  screen 
but  retained  on  the  J-mch  sieve.  The  crusher  product, 
known  as  chips,  may  ordinarily  be  used  for  this  purpose. 
The  rock  should  possess  the  same  physical  characteristics 
as  for  the  one-size  broken  stone  pavement  (§  264)  but  some- 
times no  test  limitations  for  French  coefficient  of  wear  or 
toughness  are  included  in  specifications.  The  use  of  fine 
gravel  in  place  of  broken  stone  is,  in  general,  undesirable, 
although  broken  slag  weighing  not  less  than  70  pounds  per 
cubic  foot  may  be  substituted.  Typical  specifications  of 
the  U.  S.  Bureau  of  Public  Roads  require  the  broken  stone 
aggregate  to  meet  the  following  requirements  for  size  or 
grading: 


Topeka  Type  231 

Per  cent 

Passing  ^-inch  screen,  not  less  than 95 

Retained  on  J-inch  screen,  not  less  than 80 

274.  The  Sand  Aggregate.  The  sand  aggregate  should 
be  composed  of  hard,  sharp,  uncoated  quartz  grains,  which 
will  interlock  under  compaction.  No  rigid  requirements 
for  grading  need  be  specified  provided  the  grading  of  the 
mixed  aggregate  is  properly  covered.  When  this  is  done 
inferior  sands  will  be  automatically  excluded.  It  is,  there- 
fore, necessary  to  find  a  sand  which  when  mixed  in  suitable 
proportions  with  the  broken  stone  product  will  produce  an 
aggregate  meeting  the  specification  requirements.  The  sand 
may  be  coarser  than  allowed  for  sheet  asphalt  (§  279)  but 
when  mixed  with  the  broken  stone  the  total  product  pass- 
ing the  10-mesh  sieve  should  possess  a  satisfactory  sheet 
asphalt  grading  in  order  to  produce  a  mechanically  stable 
mix.  Many  failures  of  the  Topeka  type  of  pavement  may 
be  attributed  to  lack  of  appreciation  of  this  fact.  Typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads  require 
the  sand  to  meet  the  following  limits  of  grading: 

Per  cent 

Passing  J-inch  screen 

Retained  on  200-mesh  sieve,  not  less  than ...       90 

275.  The  Asphalt  Cement.  Asphalts  (§96)  are  almost 
invariably  used  as  the  cementing  medium  for  this  type  of 
mix.  The  most  desirable  consistency  of  the  asphalt  cement 
is  harder  than  for  the  preceding  types  under  the  same  clima- 
tic conditions.  Typical  specifications  of  the  U.  S.  Bureau 
of  Public  Roads  require  a  penetration  of  from  60  to  70  for 
northern  climates  and  from  50  to  60  for  southern  climates. 
If  a  fluxed  native  asphalt  is  used  allowance  should  be  made 
for-  non-bituminous  impurities  (§§  96c,  133)  in  connection 
with  proportioning  the  mix.  While  Trinidad  asphalt  cement 
may  be  used,  most  pavements  of  this  type  are  constructed 


232     Bituminous  Concrete  and  Sheet  Asphalt 

with  either  an  oil  asphalt  or  fluxed  Bermudez  asphalt. 
Various  physical  and  chemical  requirements  commonly 
specified,  for  the  asphalt  cements  are  shown  under  Typical 
Material  Requirements  (§411). 

276.  The  Mix.  (a)  In  this  type  of  pavement  mechanical 
stability  is  largely  dependent  upon  the  grading  of  the  aggre- 
gate, most  of  which  is  fine.  For  the  material  passing  a 
10-mesh  sieve,  sand  is  to  be  preferred  to  stone  screenings 
and  the  same  grading  considerations  should,  in  general, 
govern  this  part  of  the  aggregate  as  control  sheet  asphalt 
grading.  As  the  material  passing  a  10-mesh  sieve  predomi- 
nates, the  coarser  particles"  may  be  considered  as  being 
individually  suspended  in  the  mixture  without  interlock- 
ing. From  this  standpoint  the  mix  consists  of  a  sheet  asphalt 
aggregate  carrying  coarser  particles  which  add  nothing  to 
its  stability.  As  the  pavement  is  not,  however,  ordinarily 
expected  to  withstand  as  severe  traffic  conditions  as  the 
maximum  for  sheet  asphalt  pavements,  specification  require- 
ments for  grading  are  not  usually  as  rigid.  They  should, 
however,  be  made  to  approximate  such  requirements  as 
illustrated  by  the  following  typical  specifications,  of  the 
U.  S.  Bureau  of  Public  Roads,  for  the  total  mineral  aggre- 
gate including  stone,  sand  and  mineral  filler. 

Total  Aggregate  Per  cent 

Passing  J-inch  and  retained  on  J-inch  screen     5-10 

"       i-   "       "          "         "   10-mesh  sieve  11-25 

10-mesh  and  retained  on  40-mesh  sieve  7-25 

40-     "      "         "         "  80-mesh  sieve  11-36 

"       80-     "     "         "         "200     "     P^1  10-25 

200-  "    sieve .J7-T. ..--..     5-11 

In  connection  with  the  grading  requirements  for  broken 
stone  (§  273)  and  sand  (§  274)  aggregates,  specification  re- 
quirements should  preferably  make  it  necessary  to  use  not 
less  than  10,  nor  more  than  30  per  cent,  of  broken  stone  in 
the  aggregate.  The  exact  proportions  to  use  can  only  be 


Topeka  Type  233 

ascertained  from  a  complete  sieve  test  on  each  of  the  con- 
stituents (§  249).  Such  an  aggregate  when  combined  with 
the  proper  amount  of  asphalt  cement  should  produce  a 
mixture  in  which  the  bitumen  will  usually  lie  between  7 
and  11  per  cent  and  the  mineral  filler  between  5  and  10  per- 
cent. It  will  be  noted  that  the  amount  of  total  aggregate, 
etained  on  the  10-mesh  sieve,  lies  between  16  and  35  with 
an  average  of  about  26  per  cent.  Assuming  a  fairly  well 
graded  sand  all  passing  the  10-mesh  sieve  and  containing 
36  per  cent  voids  when  compacted,  also  assuming  broken 
stone,  all  of  which  is  retained  on  the  10-mesh  sieve,  and 
which  contains  40  per  cent  voids  when  compacted,  Fig.  29 
shows  the  approximate  weights  per  square  yard  two  inches 
thick  of  the  various  constituents,  when  the  volume  propor- 
tions of  sand  to  stone  on  the  above  basis  are  3:1. 

(6)  If  Trinidad  asphalt  is  used  in  the  mix  it  is  ordinarily 
fluxed  to  proper  consistency  at  the  paving  plant,  the  propor- 
tion of  flux  to  R.A.  being  recorded  in  pounds  of  flux  per  100 
pounds  of  R.A.  The  weight  per  gallon  of  bitumen  in  the 
A.C.  will  then  vary  with  the  specific  gravity  and  proportion 
of  flux  used.  Fig.  30  shows  the  number  of  pounds  of  Trini- 
dad R.A.  to  use  in  the  same  mix  shown  in  Fig.  29  for  fluxes 
varying  in  specific  gravity  from  0.93  to  1.05  when  the  num- 
ber of  pounds  of  flux  per  100  pounds  of  R.A,  is  known. 
For  various  combinations  the  corresponding  number  of 
pounds  of  R.A.  is  indicated  at  the  intersection  of  the  diagonal 
lines  with  the  A.C.  curves.  As  the  mineral  matter  in  Trini- 
dad asphalt  may  be  considered  as  mineral  filler,  less  lime- 
stone dust  or  Portland  cement  will  be  required.  The  exact 
amount  will  be  governed  by  the  amount  of  Trinidad  R.A. 
in  the  mix  and  this  is  shown  in  the  lower  part  of  the  diagram 
for  R.A.  varying  from  17  to  27  pounds  per  square  yard. 

(c)  If  an  oil  asphalt  or  Bermudez  R.A.  is  fluxed  at  the 
plant  it  may  be  desired  to  ascertain  the  specific  gravity  of 
the  resulting  A.C.  for  use  in  connection  with  Fig.  29.  This 
may  be  calculated,  if  the  specific  gravity  of  both  flux  and 


234    Bituminous  Concrete  and  Sheet  Asphalt 

R.A.   are  known,   by  means  of  the  following  formula  in 
which  x  equals  the  specific  gravity  of  the  A.C.,  a  equals  the 


SPECIFIC  GRAVITY  OF  ROCK 

26  2.8  3.0 


60 

46 
44 
42 
40 
38 

21 

3 

20  Q 

QC 

cn 

CQ 
18 

, 

/ 

/ 

/ 

/ 

/ 

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SPECIFIC  GRAVITY  OF  ASPHALT  CEMENT 

Fig.  29     Quantities  of  Materials  Required  for  Construction  of 
Fine  Graded  Aggregate  Bituminous  Concrete  (Topeka  Type) 

specific  gravity  of  the  R.A.,  6  equals  the  specific  gravity  of 
the  flux  and  p  equals  the  number  of  pounds  of  flux  per  100 
pounds  of  R.A. 


1006  +  ap 


Topeka  Type 


235 


(d)  These  diagrams  may  be  used  as  described  for  Fig.  27 
(§  2666)  for  determining  weight  per  square  yard  and  length 


POUNDS  OF  FLUX  PER  100  POUNDS  TRINIDAD  R.A. 
20  30  40  60  60 


17 


19  21  23  25 

POUNDS  PER  SQ.  YD.  TRINIDAD  A.C. 


Fig.  30     Quantities  of  Trinidad  A.C.  Filler  Required  for  Construction 
of  Fine  Graded  Aggregate  Bituminous  Concrete  (Topeka  Type) 


of  pavement  which  should  be  laid  per  load  of  mix  of  known 
weight  (§  162).  Voids  in  the  compacted  mix/as  determined 
from  the  density  of  the  pavement  (§  384),  should  not  greatly 


236     Bituminous  Concrete  and  Sheet  Asphalt 

exceed  4  per  cent.    If  a  standard  sheet  asphalt  sand  is  used 
the  voids  may  be  as  low  as  2  per  cent. 

277.  Paint  Coats.     Before  laying  the  mix,  the  surface  of 
a  concrete  or  old  brick  foundation  is  sometimes  treated  with 
a  paint  coat  of  asphalt  cement  fluxed  or  dissolved  in  gasoline 
or  other  distillate  oil.     The  preparation  of  the  bituminous 
paint   should   be    carefully    conducted   to    prevent   fire    or 
explosion,  if  a  very  inflammable  solvent  is  used,  as  it  is  first 
necessary  to  melt  the  asphalt.     Ordinary  proportions  are 
approximately  one  part  by  volume  of  asphalt  to  two  parts 
by  volume  of  solvent.    The  paint  should  be  applied  at  the 
rate  of  not  over  0.2  gallon  per  square  yard  so  as  to  produce 
upon  drying  a  very  thin  but  uniform,  glossy  coat. 

SHEET  ASPHALT 

278.  The  Binder  Course,     (a)  The  binder  course  of  a  sheet 
asphalt  pavement  consists  of  bituminous  concrete,  composed 
of  a  mixture  of  asphalt  cement  (§  96)  with  a  single  commer- 
cial size  of  broken  stone  or  with  a  combination  of  broken 
stone  or  gravel  and  sand.    Gravel,  however,  is  not  generally 
considered  a  desirable  constituent.     The  binder  course  is 
usually  laid  to  a  compacted  thickness  of  1  or  If  inches,  the 
latter  being  preferable.     The   purpose   of  using  a  binder 
course  is  to  true  up  inequalities  in  the  foundation  surface, 
prevent  slipping  of  the  sheet  asphalt  proper,  and  to  increase 
the  stability  of  the  pavement  for  any  given  total  thickness 
above  the  foundation.    The  asphalt  cement  for  binder  is  of 
the  same  character  as  for  the  topping  (§  280)  but  is  fre- 
quently made  5  or  10  points  softer  in  penetration.    While 
sufficient  A.C.  should  be  present  to  thoroughly  bind  the 
mix,  an  excess  may  produce  fat  spots  which  will  soften  the 
overlying  topping.    If  such  fat  spots  develop  during  laying 
they  should  be  cut  out  and  replaced  with  a  suitable  mix. 
For  this  reason  somewhat  less  A.C.  is  used  in  a  binder  con- 
crete than  might  be  allowed  for  concrete  pavement  with  the 
same  grading  of  aggregate. 


Sheet  Asphalt  237 

(b)  What  is  known  as  open  binder  is  composed  of  a  broken 
stone  aggregate  without  sand.    The  quality  and  grading  of 
the  stone  may  then  be  the  same  as  described  for  one-size 
stone  bituminous  concrete  (§  264)  if  the  concrete  is  not  less 
than  1J  inches  thick.     The  approximate  quantities  of  con- 
stituents per  square  yard  1J  inches  thick  may  be  ascertained 
from  Fig.  27  (§  266)  by  multiplying  the  values  for  stone  by 
0.75  and  the  values  for  asphalt  cement  by  0.6. 

(c)  Close   binder,    now   most    commonly   used   in   sheet 
asphalt  construction,  consists  of  a  bituminous  concrete  of 
the  coarse-graded  aggregate  type,  except  that  it  is  neither 
necessary  nor  desirable  to.  prepare  so  dense  a  mix  as  to  pro- 
duce an  absolutely  smooth  voidless  surface.    It  is  not,  there- 
fore, necessary  to  use  mineral  filler  in  the  mix.     Typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads  require 
the  rock  to  have  a  toughness  (§  29)  of  not  less  than  8  and 
the  broken  stone  to  all  pass  a  1-inch  screen.    The  sand  for 
fine  aggregate  is  required  to  all  pass  a  i-inch  screen.    The 
combination  of  broken  stone  and  sand,  or  the  total  mineral 
aggregate  is  specified  to  fall  within  the  following  limits  of 
grading; 

Total  Mineral  Aggregate  Per  cent 

Passing  1-inch  and  retained  on  J-inch  screen.  .  .  .  15-65 
Passing  J-inch  sieve  and  retained  on  10-mesh  sieve  20-50 
Passing  10-mesh  sieve 15-35 

These  grading  requirements  may  usually  be  met  by  a  mix- 
ture of  approximately  5  parts  by  volume  of  clean  commer- 
cial broken  stone  with  2  parts  of  sand.  This  will  supply 
sufficient  sand  to  theoretically  fill  the  voids  of  the  com- 
pacted broken  stone  which  may  be  assumed  as  40  per  cent. 
The  amount  of  bitumen  in  the  finished  mix  will  then  usually 
run  from  4.5  to  6  per  cent.  Assuming  a  sand  with  40  per 
cent  of  voids  compacted,  Fig.  31  shows  the  approximate 
weights  per  square  yard  1J  inches  thick  of  the  various 
constituents. 


238     Bituminous  Concrete  and  Sheet  Asphalt 

If  Trinidad  asphalt  is  the  cementing  medium,  Fig.  32 
should  be  used  to  ascertain  the  number  of  pounds  of  asphalt 
cement  required,  according  to  the  amount  and  proportion 


SPECIFIC  GRAVITY  OF  ROCK 
2.4  2.6  2.8  3.0 


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SPECIFIC  GRAVITY  OF  ASPHALT  CEMENT 

Fig.  31     Quantities  of  Materials  Required  for  Construction  of 
Binder  Course 

of  flux,  as  explained  in  connection  with  Fig.  30  (§  2766). 
This  diagram  also  shows  the  corresponding  number  of 
pounds  of  R.A.  for  various  combinations  of  R.A.  and  flux. 
279.  The  Sand  Aggregate  for  Topping.  Sand  for  sheet 
asphalt  topping  should  be  hard,  clean  grained  and  mod- 
erately sharp.  The  results  of  exhaustive  investigations, 


Sheet  Asphalt 


239 


coupled  with  many  years  of  practical  experience,  have  led 
to  the  adoption  of  the  following  two  standard  gradings, 
one  for  light  and  the  other  for  heavy  traffic.  An  endeavor 


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Fig.  32     Quantity  of  Trinidad  Asphalt  Required  for 
Construction  of  Binder  Course 

is  made  in  actual  work  to  approach  one  of  these  two  stand- 
ards as  closely  as  possible,  within  certain  specified  limits. 

STANDARD  SAND  GRADINGS 


Heavy  Traffic  LightTraffic 
Per  cent          Per  cent 


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240     Bituminous  Concrete  and  Sheet  Asphalt 

A  single  sand  will  seldom  be  found  to  meet  such  specifica- 
tion limits  and  recourse  must  frequently  be  had  to  mixtures 
of  two  or  more  sands  (§  249)  in  order  to  secure  the  desired 
gracing.  Typical  specifications  of  the  U.  S.  Bureau  of 
Public  Roads,  which  are  essentially  the  same  as  the 
specifications  adopted  in  1916  by  the  American  Society 
for  Municipal  Improvements,  call  for  the  following  limita- 
tions of  grading: 

Sheet  Asphalt  Sand  Per  cent 

Passing  10  mesh  sieve -. 100 

Total  passing  10  mesh  and  retained  on  40  mesh  sieve 12-50 

Passing  10  mesh  and  retained  on  20-mesh  sieve  2-15 

"       20     "       "          "         "  30     "         «-]..,  5-15 

30     "       "          "         "  40     "        "  5-25 

"    40  "    "     "     "  so  "    "  . . . ;. ... .Y.Y.V   5-30 

"  50  "  "  "  «  80  "  "  5-40 

Total  passing  80-mesh  and  retained  on  200-mesh  sieve 20-40 

Passing  80-mesh  and  retained  on  100-mesh  sieve .  .  6-20 

"  100  "  "  "  200  "  " 10-25 

Total  passing  200-mesh  sieve 0-5 

280.  The  Asphalt  Cement.  The  most  desirable  con- 
sistency of  asphalt  cement  for  sheet  asphalt  construction 
will  depend  largely  upon  climatic  and  traffic  conditions. 
Typical  specifications  of  the  U.  S.  Bureau  of  Public  Roads 
require  a  penetration  of  from  50  to  60  for  northern  climates 
and  from  40  to  50  for  southern  climates  or  heavy  traffic. 
In  addition  to  oil  asphalts,  both  fluxed  Bermudez  and  Trini- 
dad asphalts  are  widely  used  in  sheet  asphalt  construction. 
With  both  of  the  fluxed  native  asphalts  an  allowance  for 
non-bituminous  impurities  (§§  36c,  13)  must  be  made  when 
proportioning  the  bitumen  in  the  mix.  The  fine  mineral 
matter  in  Trinidad  asphalt  is,  in  addition,  considered  as  a 
substitute  for  filler  and  this  fact  should  be  taken  into  ac- 
count in  proportioning  the  filler  if  fluxed  Trinidad  asphalt 
is  used.  Other  physical  and  chemical  requirements  com- 
monly included  in  specifications  for  the  various  asphalt 
cements  are  shown  under  Typical  Material  Requirements 
(§411). 


Sheet  Asphalt 


241 


281.  The  Topping  Mix.  (a)  The  stability  of  a  sheet 
asphalt  pavement  is  dependent  upon  the  consistency  of 
the  asphalt  cement  and  the  grading  of  the  mineral  aggre- 
gate. Mineral  filler  is  a  most  important  constituent  of 
the  mix,  and  is  usually  added  to  the  maximum  extent, 
which  will  not  interfere  with  the  workability  of  the  mix. 
Fine  sand  which  will  pass  a  200-mesh  sieve  is  not  a  suitable 
substitute  -for  filler  and  its  presence  is  undesirable.  Sand 


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SPECIFIC  GRAVITY  OF  ASPHALT  CEMENT 


1.08 


Fig.  33     Quantities  of  Materials  Required  for  Construction 
of  Sheet  Asphalt  Surface 

passing  the  80-  and  100-mesh  sieves  is,  however,  desirable 
and  the  amount  of  filler  which  the  mix  will  carry  is  largely 
dependent  upon  the  80-  and  100-mesh  sand  which  is  present. 
The  presence  of  a  certain  amount  of  relatively  coarse  grains 
such  as  the  10,  20  and  30  mesh  particles  is  highly  desirable 
in  order  to  impart  stability  to  the  mix.  An  excess  of  such 
grains,  however,  will  produce  a  coarse  open  texture  which  is 
unstable  when  subjected  to  heavy  traffic. 

(6)  The  surface  mixture  or  topping,  composed  of  sand 
meeting  the  specification  requirements  previously  given 
(§280),  will  ordinarily  carry  from  6  to  20  per  cent  of  filler 


242    Bituminous  Concrete  and  Sheet  Asphalt 

and  from  9|  to  13 \  per  cent  of  bitumen.    The  lower  limits 
are  approached  in  the  light  traffic  mixes  and  the  higher 

POUNDS  OF  FLUX  PER  100  POUNDS  TRINIDAD  R.A. 
10  20  30  40  50  30 

TT 


22  24  26  28 

POUN'DS  PER  SQ.  YD.  TRINIDAD  R.A, 

Fig.  34     Quantities  of  Trinidad  Asphalt  and  Filler  Required  for 
Construction  of  Sheet  Asphalt  Surface  Course 

limits  in  the  heavy  traffic  mixes.  For  a  reasonably  well- 
graded  sand  which  may  be  assumed  to  contain  35  per  cent 
of  voids  when  compacted,  Fig.  33  shows  the  approximate 
weights  per  square  yard,  2  inches  thick,  of  the  various  con- 


Rock  Asphalt  Pavements  243 

stituents  of  the  mix,  if  an  oil  asphalt  or  a  fluxed  Bermudez 
asphalt  is  employed  as  a  binder. 

If  Trinidad  asphalt  is  used  reference  should  be  made  to 
Fig.  34  to  ascertain  the  weight  of  A.C.  and  the  correspond- 
ing weight  of  R.A.  for  various  combinations  of  the  asphalt 
with  fluxes  of  different  specific  gravity  (§  2766).  From  the 
weight  of  R.A.  that  of  the  corresponding  amount  of  filler 
needed  is  shown  in  the  lower  part  of  the  diagram. 

(c)  If  an  oil  asphalt  or  Bermudez  R.A.  is  fluxed  at  the 
plant  the  specific  gravity  of  the  resulting  A.C.  may  be  ascer- 
tained as  previously  described  (§  276c)  and  the  value  so 
obtained  then  applied  to  Fig.  33.  These  diagrams  may  be 
used  as  described  for  Fig.  27  (§  2666)  for  determining  the 
weight  per  square  yard  and  length  of  pavement  which 
should  be  laid  per  load  of  mix  of  known  weight  (§  162). 
If  the  thickness  of  pavement  is  1|  inches  then  the  values 
shown  on  the  diagrams  should  be  multiplied  by  0.75.  Voids 
in  the  compacted  mix,  as  determined  from  the  density  of 
the  pavement  (§  384),  should  not  greatly  exceed  2  per  cent. 
They  may  be  reduced  to  0  if  the  standard  grading  for  heavy 
traffic  is  secured  and  the  proper  amount  of  bitumen  and  filler 
used. 

ROCK  ASPHALT  PAVEMENTS 

282.  Bituminous  Sandstone.  Natural  bituminous  sand- 
stones (§  100),  after  crushing  and  sometimes  heating  in  a 
revolving  drum,  have  been  used  to  a  limited  extent  in  the 
construction  of  sheet  pavements.  Such  pavements,  in 
general,  resemble  artificial  sheet  asphalt  but,  owing  to 
variations  in  the  natural  product,  are  apt  to  be  less  uniform 
and  to  possess  a  less  desirable  sand  grading.  Specifications 
for  bituminous  sandstones  usually  covered  the  grading 
limitations  of  the  mineral  aggregate  and  the  per  cent  of 
bitumen  which  must  be  present.  Samples  should,  therefore, 
be  taken  from  each  shipment  and  no  sample  should  repre- 
sent more  than  50  tons.  These  samples  should  be  sub- 


244     Bituminous  Concrete  and  Sheet  Asphalt 

jected  to  laboratory  examination  before  the  material  is 
used.  Sometimes  specification  requirements  can  only  be 
met  by  an  admixture  of  two  or  more  grades  of  rock  asphalt 
or  by  the  addition  of  flux  or  asphalt  cement,  in  which  case 
plant  inspection  may  involve  determinations  of  the  per  cent 
of  bitumen  in  the  product  (§  133),  in  addition  to  grading 
tests  of  the  extracted  mineral  aggregate.  The  same  general 
considerations  governing  sheet  asphalt  construction  should 
apply  to  pavements  constructed  of  rock  asphalt  of  the  bitu- 
minous sandstone  type. 

283.  Bituminous    Limestone.      Bituminous     limestones 
(§  100)  are  usually  crushed  down  to  the  state  of  fine  powder 
before  being  used  in  the  construction  of  the  sheet  type  of 
pavement.    In  such  products  grading  of  the  mineral  matter 
does  not  appear  to  be  a  matter  of  moment  as  each  fine 
particle  is  impregnated   with  asphalt   and   coalesces   with 
its  neighboring  particles,  under  compaction,  to  produce  a 
dense  tough  mastic  highly  resistant  to  displacement  under 
traffic.    The  powder  is  heated  in  a  revolving  drum  or  open 
pan  to  a  temperature  of  approximately  300°  F.  after  which 
it  is  spread  and  compacted  as  in  sheet  asphalt  construction. 
Hand  tamping  is,  in  addition,  highly  desirable  in  order  to 
secure  maximum  compaction.    As  in  the  case  of  bituminous 
sandstone,  it  may  be  necessary  to  combine  two  or  more 
grades  of  the  rock  asphalt  or  to  add  flux  or  asphalt  in  order 
to  secure  a  uniform  product.     Specification  requirements 
for  this  type  usually  call  for  the  presence  of  from  9  to  12 
per  cent  of  bitumen.    This  can  only  be  ascertained  by  means 
of  a  laboratory  test  (§  133).     A  sample  should,  therefore,  be 
taken  for  each  50  tons  of  product  and  subjected  to  labora- 
tory test  before  the  material  is  used. 

10} 

BITUMINOUS  EARTH  PAVEMENTS 

284.  The  Mineral  Aggregate.     Pavements  constructed  of 
a  mixture  of  earth  and  asphalt  cement  have  barely  passed 


Bituminous  Earth  Pavements  245 

the  experimental  stage,  so  that  information  relative  to  the 
best  type  of  earth  for  the  mix  is  limited.  In  general,  how- 
ever, it  appears  that  the  finer  the  state  of  subdivision  the 
better.  A  pure  clay  should,  therefore,  prove  to  be  the  best 
type.  Such  a  product  thoroughly  mixed  or  impregnated 
with  asphalt  appears  to  possess  properties  similar  to  the 
finely  crushed  natural  bituminous  limestones  (§  283)  in  which 
the  exact  grading  of  the  mineral  parcticles  does  not  seem  to 
be  of  great  importance.  Before  admixture  with  the  asphalt, 
all  clumps  of  mineral  particles  should  be  broken  up  and,  in 
the  National  Pavement,  which  is  patented,  this  is  accom- 
plished by  passing  the  earth  through  a  heating  drum  equipped 
with  a  special  disintegrating  device.  Specifications  for  this 
pavement  require  the  pulverized  earth  to  conform  to  the 
following  limitations: 

Per  Cent 

Passing  20-mesh  and  retained  on    50-mesh  sieve. .  .      0-20 
"     •  50-    "       "          "         "  200-    "        '(.....      0-30 

"     200-    "     sieve 50-100 

In  addition,  the  earth  is  required  to  develop  a  tensile  strength 
of  not  less  than  50  pounds  per  square  inch  when  mixed  to  a 
stiff  paste  with  water,  molded  in  a  cement  briquette  mold 
(§  81)  and  allowed  to  dry.  Upon  ignition  at  a  red  heat  it 
is  required  to  lose  from  3  to  12  per  cent.  It  is  further  re- 
quired to  be  soluble  in  dilute  1  : 2  hydrochloric  acid  to  the 
extent  of  from  5  to  15  per  cent  but  to  contain  not  more  than 
5  per  cent  of  carbonates.  The  value  of  specifying  such  prop- 
erties, which  can  only  be  determined  by  laboratory  test,  is 
still  a  matter  of  speculation,  due  to  the  limited  amount  of 
service  data  which  is  available. 

285.  The  Asphalt  Cement.  The  consistency  of  asphalt 
cement  used  in  bituminous  earth  mixtures  is  much  softer 
than  for  sheet  asphalt  and  in  fact  is  the  same  or  nearly  the 
same  as  for  bituminous  macadam.  Specifications  for  the 
National  Pavement  call  for  an  asphalt  cement  of  from  80 
to  150  penetration,  depending  upon  the  fineness  of  the  pul- 


246     Bituminous  Concrete  and  Sheet  Asphalt 

verized  earth,  traffic  and  local  climatic  conditions.  Best 
results,  so  far  obtained,  appear  to  have  been  secured  with 
an  asphalt  cement  of  about  90  penetration  in  combination 
with  a  soil,  80  per  cent  of  which  would  pass  the  200-mesh 
sieve. 

286.  The  Mix.     Specifications  for  the  National  Pavement 
require  the  mix  to  contain  from  15  to  20  per  cent  of  bitu- 
men.   Within  these  limits  the  finer  the  texture  of  the  soil 
the  more  bitumen  will  be  required.    The  weight  per  square 
yard  for  asphalt  earth  mixtures  2  inches  thick  compacted 
will  vary  with  the  specific  gravity  and  proportion  of  the 
constituents,  as  in  the  case  of  other  mixtures,  but  will  approxi- 
mate 180  pounds.    Upon  the  basis  of  17  per  cent  of  bitumen 
this  will  represent  30.6  pounds  of  asphalt  cement  and  149.4 
pounds  of  dry  soil  per  square  yard. 

MAINTENANCE 

287.  Methods,     (a)  Ordinary  maintenance  of  bituminous 
concrete  pavements,  originally  constructed  with  a  seal  coat, 
involves  surface  treatment  with  bituminous  material  and 
cover  exactly  as  described  for  bituminous  macadam  (§  206a) . 
Holes  and  depressions  for  all  types  should  be  remedied  by 
cutting  out  the  pavement  so  as  to  produce  excavations  with 
approximately  vertical   sides   for   the   entire   thickness   of 
wearing  course.    The  excavation  should  then  be  thoroughly 
cleaned  and  filled  with  a  hot  bituminous  mixture  .of  the 
same  kind  as  used  in  original  construction,  which  should 
be  thoroughly  tamped  to  produce  smooth  even  joints  with 
the  surrounding  area.     For  the  coarse  aggregate  type  of 
pavement,  patches  are  occasionally  made  with  a  mixture  of 
broken  stone  and  emulsified  asphalt  or  cut-back  tar  (§§  333, 
334). 

(6)  Cracks,  in  bituminous  concrete  pavements  containing 
relatively  large  fragments  of  broken  stone,  are  of  less  com- 
mon occurrence  than  in  pavements  of  the  sheet  type.  In 


Maintenance  247 

the  latter  they  are  sometimes  due  to  contraction  cracks 
formed  in  the  underlying  concrete  foundation  and  some- 
times to  the  use  of  too  little  or  too  hard  a  bitumen  in  the 
mix.  They  are  difficult  to  repair  satisfactorily  and,  in 
general,  had  better  be  left  alone  until  the  edges  begin  to  dis- 
integrate and  wear  away.  A  patch  may  then  be  made  by 
cutting  out  the  pavement  on  both  sides  of  the  crack  and  filling 
with  fresh  mix.  The  sides  of  the  hole  are  sometimes  lightly 
painted  with  hot  bituminous  cement  before  the  new  mix  is 
tamped  into  place.  Great  care  should  be  exercised  to  ob- 
tain a  well-bonded  joint  or  two  cracks,  one  on  each  side  of 
the  patch,  are  likely  to  develop  in  place  of  the  one  original 
crack. 

(c)  General  waviness  is  usually  due  to  an  unstable  founda- 
tion, the  presence  of  a  poorly  graded  aggregate,  or  to  the 
use  of  too  much  or  too  soft  a  bituminous  cement.    This  con- 
dition is  practically  impossible  to  remedy  without  recon- 
structing or  resurfacing  the  pavement.     Failures   due  to 
foundation  causes  should  be  remedied  by  removal  and  re- 
placement of  the  foundation  wherever  repairs  are  required 
in  the  pavement  proper. 

(d)  In  the  sheet  types  of  pavement,  maintenance  by  re- 
surfacing is  sometimes  accomplished  by  means  of  the  sur- 
face  heater   method.     The   surface   heater   consists   of   an 
apparatus  for  bringing  hot  air  or   superheated  steam  into 
contact   with   the   pavement   until   the   old   mix   has   been 
softened  to  the  desired  depth.    All  burned  material  is  then 
removed  from   the  heated   area  and   immediately  replaced 
with  fresh  hot  mix  which   is  spread  and  compacted  as  in 
original   construction.     Such  method   of   repairing  should, 
of  course,  be  limited  to  cases  involving  failure  of  the  wearing 
course  only,   in . which  disintegration  has  progressed  from 
the  top  down  and  not  from  the  bottom  up. 

288.  Inspection.  Inspection  of  maintenance  by  seal  coat- 
ing will  usually  be  the  same  as  for  surface  treatment  (Chap- 
ter IX).  For  patching  it  will  be  the  same  as  for  original 


248     Bituminous  Concrete  and  Sheet  Asphalt 

construction  and  may  involve  both  plant  and  street  inspec- 
tion depending  upon  the  extent  of  repairs  and  the  quantities 
of  materials  used. 


INSPECTOR'S  EQUIPMENT 

289.  Construction.  For  construction  work  involving  the 
use  of  small  portable  paving  plants,  the  street  Inspector  may 
also  be  required  to  act  as  plant  Inspector,  in  which  case  he 
will  require  certain  equipment  listed  under  the  Plant  Labora- 
tory (§  253),  in  addition  to  that  needed  on  the  street.  Ordi- 
narily, however,  where  both  plant  and  street  Inspectors 
are  employed  the  latter  will  find  the  following  sufficient  for 
his  work. 

For  Measurements: 

A  50-foot  steel  tape. 

A  pocket  rule  (§387). 

A  stout  screw  driver  or  2-inch  putty  knife. 
For  Sampling: 

A  supply  of  tin  or  wooden  boxes  for  holding  samples  of 
the  mix.  (An  ordinary  cigar  box  is  sufficiently  large 
for  all  but  very  coarse  aggregate  with  fragments 
greater  than  1  inch  in  diameter.) 

A  supply  of  gum  labels  for  identification  information. 

A  few  very  stout  boxes  may  be  required  occasionally 
for  packing  samples  of  compressed  pavement  about 
1  foot  square. 

A  supply  of  1  quart  tin  cans  for  seal  coat  or  paint  coat 

materials. 
For  Testing: 

An  armored  thermometer  (§  386) . 

1  Two  field  screens  (§  371)  as  may  be  called  for  by  speci- 
fications for  seal  coat  cover. 

1  Ordinarily  this  apparatus  may  be  dispensed  with,  provided 
samples  of  seal  coat  cover  are  taken  by  the  street  Inspector  and  tested 
by  the  plant  Inspector  before  use. 


Inspector's  Equipment  249 

*A   spring  balance   with   pan   capacity  of   10   pounds 
if  seal  coat  cover  is  to  be  tested  (§  371). 

For  Records  and  Reports: 
A  field  diary  and  pencil. 
A  supply  of  report  forms  (§  404) . 
A  carbon  paper  for  duplication  of  reports. 

290.  Maintenance.  For  maintenance  the  street  Inspec- 
tor's equipment  may  be  the  same  as  for  surface  treatment 
with  carpeting  mediums  (§  191)  or  it  may  be  as  complete  as 
that  required  for  original  construction,  depending  upon  the 
character  and  volume  of  work.  If  extensive  repairs  to  con- 
crete foundation  are  involved,  additional  equipment  listed 
under  construction  of  concrete  pavements  (§  233)  may  be 

required. 

1  Ibid. 


CHAPTER  XIV 

INSPECTION  OF  BRICK  AND  BLOCK 
PAVEMENTS 

GENERAL  CHARACTERISTICS 

291.  Types  of  Pavements,  (a)  Brick  and  block  pave- 
ments are  most  commonly  classified  according  to  the  ma- 
terial of  which  they  are  composed.  These  are: 

Vitrified  shale  or  clay. 

Slag. 

Stone. 

Bituminous  Concrete  (commonly  known  as  asphalt 

block). 
Creosoted  Wood. 

During  manufacture  the  material  is  molded  or  cut  into 
approximately  rectangular  shapes  of  the  same  size  and 
dimensions  and  the  pavement  proper  is  usually  laid  in  regu- 
lar courses  so  as  to  break  joints  between  the  courses.  An 
exception  to  this  method  is  found  in  the  use  of  small,  irregu- 
lar, but  approximately  cubical  stone  block,  known  as  irregu- 
lar sets,  which  are  laid  in  circular  arcs. 

(b)  Brick  and  block  are  sometimes  laid  upon  a  cushion 
or  bed  of  sand  resting  upon  the  foundation  and  sometimes 
upon  a  mixture  of  sand  and  Portland  cement.  In  addition 
to  the  name  of  the  material  proper,  such  pavements  are 
known  as  sand  cushion  or  mortar  cushion  pavements.  When 
brick,  stone  or  slag  blocks  are  laid  directly  upon  a  green 
concrete  foundation  so  as  to  be  held  in  place  by  the  con- 
crete as  it  sets,  the  pavement  is  commonly  termed  mono- 

250 


Details  of  Construction  251 

lithic.  When  a  concrete  foundation  has  already  set  but  the 
brick  or  block  are  bonded  to  it  by  the  use  of  a  cement-sand 
or  mortar  cushion,  the  pavement  is  said  to  be  semi-mono- 
lithic. In  both  the  monolithic  and  semi-monolithic  types 
a  cement  mortar  grout  is  used  to  fill  joints  between  the 
brick  or  block. 

(c)  Brick  and  block  pavements  are  also  frequently  de- 
scribed by  the  material  used  in  filling  joints.  This  may  be 
cement  mortar  grout,  poured  asphalt  or  tar  pitch,  or  a  bitu- 
minous grout  composed  of  a  mixture  of  bituminous  material 
and  sand.  Less  frequently  sand  or  fine  gravel  only  are 
used  to  fill  joints. 

292.  General  Methods  of  Construction.     Unless  a  green 
concrete  foundation  is  used,  the  foundation  is  first  covered 
with  a  cushion  or  bed  of  sand,  or  sand  and  cement,  to  true 
up  surface  inequalities   and   provide  an  adjustable   setting 
which  will  permit  the  top  surfaces  of  the  block  to  be  brought 
flush  with  one  another  under  compaction.     The  blocks  are 
then  laid  by  hand  upon  this  bed  in  straight  courses,  at  right 
angles  to  the  center  line  of  the  pavement  so  as  to  break 
joints  between  adjacent  courses.     If  a  joint  filler  is  to  be 
used  lugs  or  projections  on  one  side  and  end  of  the  block 
serve  to  produce  uniform  spacing.     After  the  blocks  have 
been  laid  the  pavement  is  rolled  to  true  up  the  surface  and 
bring  every  block  to  a  firm  bedding.    If  a  joint  filler  is  needed ' 
it  is  then  poured  or  broomed  into  the  joints  between  the 
blocks  so  as  to  completely  fill  them  from  the  bottom  up. 
The  pavement  may  then  be  opened  to  traffic  except  in  the 
case  of  a  cement  grout  filler  which  requires  protection  for 
a  period  of  not  less  than  7  days. 

DETAILS   OF  CONSTRUCTION  APPLICABLE  TO 
ALL  TYPES 

293.  Foundations.     While  in  some  instances  brick  and 
block  pavements  have  been  laid  upon  broken  stone,  slag  or 


252  Brick  and  Block  Pavements 

gravel  foundations,  and  even  upon  the  natural  soil  with  the 
use  of  a  sand  cushion,  it  is  generally  conceded  that  a  cement 
concrete  foundation  (§219)  is  the  most  suitable  type.  The 
construction  of  a  concrete  foundation  for  such  pavements 
is  the  same  as  for  any  other,  the  only  modification  being 
that  of  the  monolithic  brick  pavement.  In  this  type  great 
care  should  be  exercised  in  making  the  concrete  of  uniform 
consistency,  and  the  foundation  surface  as  true  and  smooth 
as  possible.  As  the  foundation  construction  is  then  imme- 
diately followed  by  laying  and  rolling  the  brick,  it  is  essen- 
tial that  it  be  kept  no  further  in  advance  of  the  brick  laying 
than  will  be  required  to  firmly  bed  the  brick  before  initial 
set  has  occurred. 

294.  Cushions  or  Beds,  (a)  When  a  plain  sand  cushion 
is  used,  it  is  spread  over  the  clean  foundation  so  as  to  pro- 
duce the  compacted  depth  which  is  specified,  usually  1, 
1J  or  2  inches.  The  sand  should  all  pass  a  J-inch  screen  and 
should  contain  not  over  5  per  cent  removed  by  the  elutria- 
tion  test.  At  least  one  sample  from  each  shipment  of  sand 
(§  60)  should  be  taken  and  tested  before  use.  The  cushion 
should  be  shaped  to  the  desired  cross  section  by  means  of 
a  template  and  then  rolled  with  a  hand  roller,  weighing  not 
less  than  10  pounds  per  inch  width  of  tread  and  provided 
^with  a  handle  not'  less  than  12  feet  long.  During  rolling 
the  sand  should  be  slightly  moist  and  a  light  sprinkling 
with  water  may  be  necessary.  After  initial  compaction, 
the  cushion  should  be  reshaped  and  rerolled  until  firm  and 
true  to  the  required  cross  section.  It  should  be  prepared 
about  50  feet  in  advance  of  the  brick  or  block  laying  and 
should  not  be  walked  upon  or  disturbed  after  final  shaping. 
If  displaced  by  any  cause  it  should  be  carefully  reshaped 
and  compacted  before  the  brick  are  placed. 

(b)  Cement-sand  beds  are  composed  of  a  dry  mixture 
or  cement  and  sand  in  specified  proportions,  usually  1  : 3 
or  1:4.  The  mix  is  preferably  prepared  in  a  mechanical 
batch  mixer  and  should  be  of  uniform  quality  and  color. 


Details  of  Construction 


253 


It  is  spread  upon  the  clean  foundation  to  produce  the 
specified  compacted  depth,  usually  i  or  1  inch.  It  is  then 
shaped  and  rolled  as  described  for  sand  cushion,  without 


10 


15  20  25  30 

WIDTH  OF  PAVEMENT,  FEET 


Fig.  35      Quantities  of  Materials  Required  for  Construction  of  Cushions 

the  use  of  water.  The  bed  is  later  set  by  a  sprinkling  of 
water  after  the  blocks  have  been  laid.  Sometimes,  however, 
the  bed  is  sprinkled  just  before  they  are  laid.  No  more 
of  this  type  of  bed  should  be  laid  in  advance  than  can 
be  covered  during  the  working  period  The  sand  should 


254  Brick  and  Block  Pavements 

all  pass  a  i-inch  screen  and  show  not  more  than  5  per  cent 
removed  by  the  elutriation  test  (§  536).  At  least  one  sample 
of  sand  and  cement  should  be  taken  and  tested  before  use. 

(c)  Occasionally  specifications  call  for  the  use  of  a  damp 
or  wet  mortar  bed  to  be  laid  just  prior  to  setting  the  block. 
In  such  cases  the  same  proportions  of  cement  and  sand  are 
used  as  mentioned  in  the  preceding  paragraph.  A  fourth 
variety  of  bed,  used  to  a  limited  extent  in  connection  with 
wood  block  pavements,  consists  of  mortar  which  is  allowed 
to  set  and  is  afterwards  painted  with  hot  tar  before  the 
wood  block  are  laid.  Fig.  35  shows  the  approximate  quanti- 
ties of  materials  required  to  lay  a  sand  cushion  1J  inches 
thick,  a  1  :  3  cement-sand  cushion  1  inch  thick,  and  a  mortar 
bed  \  inch  thick,  per  100  linear  feet  of  pavement  of  various 
widths. 

295.  Laying  the  Brick  or  Block.  Brick  and  block  are 
usually  laid  by  hand  in  parallel  rows,  at  right  angles  to 
the  center  line  of  the  pavement,  so  as  to  break  joints  at 
least  3  inches.  If  the  block  are  provided  with  lugs  or  pro- 
jections they  are  laid  so  that  such  projections  have  the  same 
relative  position,  thus  forming  continuous  transverse  joints. 
On  curves  and  at  intersections  the  blocks  are  often  laid  at 
an  angle  to  the  center  line  according  to  various  designs. 
Each  block  should  be  carefully  set  so  as  to  be  firmly  bedded 
and  uniformly  spaced  with  relation  to  adjacent  blocks.  The 
courses  should  be  kept  as  straight  as  possible  and,  if  they 
tend  to  curve  or  wave,  they  may  be  straightened  by  lightly 
striking  a  4-by  4-inch  timber,  about  three  feet  long,  placed 
against  every  fourth  course.  Cut  or  broken  block,  known 
as  bats,  should  be  used  only  at  or  near  the  ends  of  courses 
to  fill  in  spaces  too  small  to  hold  full  size  block.  Bats  should 
have  clean  sharp  edges  so  formed  as  to  produce  neat  joints 
with  the  surrounding  blocks.  If  a  joint  filler  is  to  be  used, 
all  spaces  between  the  blocks  should  be  kept  open  and  clean 
from  the  bottom  up  until  the  filler  is  applied.  With  block, 
which  vary  materially  in  depth,  considerable  skill  is  re- 


Details  of  Construction  255 

quired  to  bed  them  so  that  a  surface,  true  to  crown  and 
grade,  will  be  obtained  after  compaction.  This  may  at 
times  require  slight  adjustment  in  the  thickness  of  cushion 
under  individual  block  but,  in  general,  after  the  cushion  is 
once  shaped  and  compacted,  it  should  be  disturbed  as  little 
as  possible.  Except  for  stone  block  the  pavers  should 
never  stand  on  the  cushion,  but  on  block  which  have 
already  been  laid.  Immediately  after  laying  and  beforo 
compaction,  the  surface  of  the  pavement  should  be  in- 
spected and  all  imperfect  block  which  fail  to  meet  specifi- 
cation requirements  should  be  culled  out  and  replaced. 

296.  Compaction,  (a)  With  the  exception  of  asphalt 
block,  set  in  a  mortar  bed,  all.  block  pavements  are  rolled 
or  rammed  to  produce  a  smooth  uniform  surface  and  firm 
setting.  In  the  case  of  a  cement-sand  or  mortar  bed,  final 
compaction  should  be  obtained  before  the  bed  has  had 
an  opportunity  to  set.  Brick,  slag  block,  irregular  stone 
sets  or  Durax,  and  wood  block  are  rolled  after  the  surface 
has  been  swept  free  of  loose  fragments  or  spalls.  A  tandem 
roller  weighing  from  three  to  five  tons  is  ordinarily  used. 
Rolling  is  begun  at  and  parallel  to  one  side  and  progresses 
slowly  to  the  center  line,  after  which  the  operation  is  re- 
peated from  the  other  side.  Block  adjacent  to  gutters  are 
frequently  hand  tamped.  After  initial  compaction  has 
been  secured  the  speed  of  the  roller  is  increased  and  the 
pavement  rolled,  at  an  angle  of  45  degrees  to  the  center  line, 
first  in  one  direction  and  then  the  other.  All  block  broken 
or  injured  by  rolling  should  be  immediately  removed  and 
carefully  replaced  by  new  block,  so  as  to  produce  a  uniform 
surface.  If  at  any  place  the  cushion  is  forced  up  between 
the  block,  for  a  depth  of  over  \  inch,  the  block  should  be 
removed  and  relaid  after  reshaping  and  compacting  the 
cushion. 

(6)  In  regular  stone  block  paving,  each  individual  block 
should  be  rammed  to  a  firm  even  bed  by  striking  the  block 
squarely  in  the  center  of  its  surface.  The  rammers  usually 


256  Brick  and  Block  Pavements 

weigh  between  35  and  50  pounds.  After  ramming,  blocks 
which  have  been  forced  below  the  finished  grade  should  be 
removed  with  tongs  so  as  not  to  disturb  the  bedding  or 
position  of  adjacent  block.  They  are  then  relaid  with  the 
addition  of  cushion  material,  and  rammed.  Pinch  bars 
should  not*  be  used  to  remove  block.  Ordinarily,  stone 
block  should  be  rammed  soon  after  laying  and  not  more 
than  25  feet  behind  the  laying. 

297.  Joint  Filling,  (a)  Plain  sand  filler  is  at  present 
almost  exclusively  limited  to  asphalt  block  pavements, 
which  are  laid  with  as  close  joints  as  possible.  In  such 
pavements,  as  soon  as  the  block  are  laid  they  should  be 
covered  with  fine,  dry,  clean  sand  which  will  pass  a  10-mesh 
sieve.  The  sand  should  be  swept  into  the  joints  and  an 
excess  allowed  to  remain  on  the  surface  of  the  pavement 
until  traffic  has  completely  filled  or  closed  the  joints. 

(b)  Cement  grout  filler  for  brick,  slag  block  and  stone 
block  pavements  is  composed  of  equal  parts  by  volume  of 
cement  and  sand  mixed,  preferably  in  a  batch  mixer,  with 
water  to  a  thin  creamy  consistency  which  will  permit  it  to 
flow  readily  into  the  joints  and  fill  them  from  the  bottom 
up,  but  not  so  thin  that  the  sand  and  cement  will  separate. 
To  prevent  such  separation  the  grout  should  be  constantly 
agitated  until  it  is  flooded  over  the  pavement  which  is  first 
sprinkled  with  water.  It  is  then  broomed  into  the  joints 
until  flush  with  the  surface.  As  the  grout  shrinks  additional 
grout  is  broomed  in  until  the  joints  will  take  no  more,  after 
which,  all  excess  is  squeegeed  off  of  the  pavement.  Metal 
strips  TV  of  an  inch  thick,  6  inches  wide  and  not  less  than 
3  feet  long  should  be  inserted  between  the  blocks,  across 
the  pavement  to  close  a  stretch  of  grouting,  with  a  straight 
joint  at  the.  end  of  each  working  period.  As  soon  as  the 
grout  has  reached  its  initial  set,  the  pavement  should  be 
covered  with  J  inch  or  more  of  clean  sand.  It  should  then 
be  sprinkled  two  or  three  times  a  day  to  prevent  the  grout 
from  drying  out  too  rapidly.  At  the  end  of  a  week  or  ten 


Details  of  Construction  257 

days  the  sand  covering  may  be  removed.  Grouting  sand 
should  consist  of  clean  hard  quartz  grains.  Typical  speci- 
fications of  the  U.  S.  Bureau  of  Public  Roads  require  it  to 
meet  the  following  grading  limitations: 

Per  cent 

Passing  10-mesh  sieve 100 

20-    "        "    ,  not  less  than 80 

"      100-    "  "    more  than 10 

These  specifications  further  require  that  it  show  not  more 
than  5  per  cent  removed  by  the  elutriation  test  (§  536)  and 
that  it  develop  a  mortar  tensile  strength  (§  58)  of  at  least 
75  per  cent  of  that  developed  by  standard  mortar.  At  least 
one  sample  of  grouting  sand  should  be  taken  from  each 
shipment  and  tested  before  use.  Cement  should  meet 
the  usual  standard  specifications  (§§  65-67),  and  each 
shipment  should  be  sampled  and  tested. 

(c)  Hot  poured  bituminous  fillers  may  be  used  for  all 
types  of  brick  and  block  with  the  exception  of  asphalt 
block.  For  brick,  slag  block  and  stone  block,  an  asphalt 
filler  of  the  blown  type  (§  97)  is  most  commonly  used. 
Typical  specifications  of  the  U.  S.  Bureau  of  Public  Roads 
require  that  such  a  filler  show  a  melting  point,  by  the  ring 
and  ball  method  (§  126),  of  not  less  than  80°  C.  and  a  pene- 
tration (§  125)  at  25°  C.  of  from  30  to  50.  The  penetration 
at  0°  C.  is  specified  at  not  less  than  20,  and  at  46°  C.  at  not 
more  than  100.  For  wood  block  pavements,  a  tar  pitch 
filler  (§  104)  is  most  commonly  used.  The  1916  specifica- 
tions of  the  American  Society  for  Municipal  Improvements 
require  that  such  a  filler  show  a  melting  point,  cube  method 
in  water,  of  from  60°  to  66°  C.  and  that  it  contain  from  22 
to  37  per  cent  of  free  carbon  (§  133).  Other  physical  and 
chemical  properties  of  asphalt  and  tar  fillers  commonly 
specified  are  given  under  Typical  Material  Requirements 
(§§411,  413).  The  general  method  of  applying  hot  poured 
bituminous  fillers  is  the  same  as  for  expansion  joints  (§§  328, 


258  Brick  and  Block  Pavements 

329)  except  that  sometimes  an  excess  of  filler  is  used  to 
flood  the  surface  and  upon  squeegeeing  to  produce,  with  the 
later  application  of  mineral  cover  (§  184),  a  bituminous  mat 
or  carpet  (§  178)  over  the  entire  pavement.  At  least  one 
sample  of  bituminous  filler  and  cover  should  be  taken  from 
each  shipment  and  tested  before  use. 

(d)  Bituminous  grout  or  mastic  fillers  are  sometimes  used 
for  filling  joints  in  stone  block  and  brick  pavements.  Such 
mastic  is  prepared -by  mixing  hot  sand  and  bituminous  ma- 
terial in  such  proportions  as  to  produce  a  thin  grout  which, 
at  the  temperature  of  application,  is  sufficiently  fluid  to 
flow  into  the  joints  and  completely  fill  them.  The  mixture 
is  made  up  by  hand  in  small  batches  in  steel  wheel  barrows 
and  will  ordinarily  carry  from  40  to  60  per  cent  by  volume 
of  bituminous  material.  The  sand  should  be  of  the  same 
grade  and  quality  as  for  cement  grout  (§2976).  For  use 
with  tar  it  should  be  heated  to  between  250  and  325°  F. 
and  with  asphalt  to  between  325  and  400°  F.  For  tar 
pitch  the  1916  specifications  of  the  American  Society  for 
Municipal  Improvements  require  a  melting  point,  cube  in 
water  method,  of  from  46°  to  57°  F.  and  from  20  to  35  per 
cent  of  free  carbon  (§  133).  For  asphalt  a  melting  point 
(§  126)  of  from  54°  to  63°  C.  is  required  and  a  penetration 
(§  125)  at  25°  C.  of  from  60  to  100.  Other  physical  and 
chemical  properties  commonly  specified  for  both  tar  and 
asphalt  are  given  under  Typical  Material  Requirements 
(§413).  Whichever  bituminous  material  is  used,  the  tem- 
perature to  which  it  is  heated  should  lie  between  the  tem- 
perature limits  given  for  sand.  Immediately  after  mixing, 
the  bituminous  grout  should  be  flooded  upon  the  pavement 
surface  and  squeegeed  into  the  joints  before  it  has  had  an 
opportunity  to  harden.  Great  care  should  be  exercised  to 
fill  all  joints  from  the  bottom  up.  As  little  excess  grout  as 
possible  should  be  left  on  the  surface  of  the  pavement  and 
whatever  remains  should  be  covered  with  a  light  coat  of  the 
hot  sand.  At  least  one  sample  of  bituminous  material  and 


Vitrified  Shale  and  Clay  Brick  259 

sand  should  be  taken  from  each  shipment  and  tested  before 
use. 

298.  Expansion    Joints.     Expansion    joints    for    cement 
grouted  pavements  are  commonly  placed  along  curbs  or 
gutters  and  sometimes  extend  through  the  entire  thickness 
of  pavement  and  concrete  foundation.     Transverse  expan- 
sion joints    are    also    sometimes    inserted,   particularly    at 
street  intersections.    Bituminous  fillers  are  specified  for  fill- 
ing expansion  joints  and  the  application  and  properties  of 
such  fillers  are  described  later  (§§  328-330). 

299.  Hillside  Construction.     In  order  to  reduce  slipperi- 
ness  on  heavy  grades,  special  forms  of  block  and  brick  are 
often  used.     Such  block  may  have  one  long  edge  on  the 
upper  face  beveled,  or  the  upper  face  may  be  corrugated, 
grooved  or  ridged.    After  filling  joints  between  such  block, 
the  filler  is  broomed  out  of  the  depressions,  joints  or  grooves 
for  a  sufficient  depth  to  insure  foothold  for  horses. 

300.  Measurement.     Brick    and    block    pavements    are 
commonly  measured  and  paid  for  upon  a  square  yard  basis, 
complete  in  place,  including  brick  or  block,  cushion,  filler 
and    expansion    joints.      Sometimes,    however,    bituminous 
materials  are  paid  for  as  a  separate  item,  in  which  case  the 
Inspector,   in  addition  to  measurements  of  length,   width 
and  depth  of  pavement  and  blocks,  should  keep  track  of 
the  amount  of  bituminous  material  used.     He  should  also 
keep  track  of  the  actual  and  relative  volumes  of  all  con- 
stituents of  grout  fillers  and  mortar  cushions  or  beds.    Under 
the  various  types  of  brick  and  block  in  the  following  para- 
graphs, diagrams  are  given  which  may  be  of  service  in  the 
matter  of  measurement. 

VITRIFIED   SHALE  AND   CLAY  BRICK 

301.  Types  of  Brick,     (a)  Paving  brick  are  manufactured 
either  from  fire-clay  or  an  intimate  mixture  of  shale  and 
fire-clay.     The  latter   are  known  as  shale  brick  and    are 


260  Brick  and  Block  Pavements 

usually  dark  brown  or  red  in  color,  while  the  fire-clay  brick 
are  buff  or  yellow.  The  raw  material,  after  proper  reduc- 
tion or  grinding,  is  mixed  with  water  to  produce  a  thick 
slurry  or  paste  which  is  forced  through  dies  or  formers  and 
emerges  as  an  approximately  rectangular  column  or  ribbon. 
The  individual  brick  are  formed  by  cutting  off  sections  of 
the  ribbon  to  the  desired  thickness.  The  green  brick  are 
then  allowed  to  dry,  after  which  they  are  stacked  in  kilns 
and  burned  to  incipient  vitrification.  They  are  then  slowly 
cooled  or  annealed.  The  manufacturing  process  requires 
careful  selection  of  materials,  and  control  of  details,  in 
order  to  produce  brick  which  are  hard,  regular  in  shape 
and  free  from  undesirable  checks,  cracks  and  kiln  marks. 
There  are  three  main  types  of  paving  brick,  which  are  classi- 
fied according  to  certain  details  of  manufacture,  as  repressed 
brick,  wire-cut  lug  brick  and  vertical  fiber  brick. 

(6)  Repressed  brick  are  made  by  repressing  the  green 
brick  in  suitable  molds  before  they  are  burned.  Under 
repressing,  lugs  may  be  formed  and  the  edges  rounded. 
Sometimes  raised  letters  or  trade  marks  which  serve  as  lugs 
are  formed  by  the  molds,  and  sometimes  the  letters  are 
depressed. 

(c)  Wire-cut  lug  brick  are  formed   by  cutting  the  clay 
ribbon,  by  a  patented  process,  so  as  to  produce  lugs  on  one 
of  the  cut  surfaces  of  the  brick.     The  cut  surfaces,  which 
are  sometimes  rough  and  porous,  then  form  the  sides  of 
the  brick,  as  laid,  while  the  wearing  surface  has  the  smooth 
dense  finish  left  by  the  mold. 

(d)  In  the  manufacture  of  vertical  fiber  brick,  the  ribbon 
of  clay  is  cut  straight  through  and  the  lugs,  if  made,  are 
formed  by  the  die  through  which  the  clay  is  forced.     The 

r  wearing  *  surf  ace  of  such  brick  will  then  be  one  of  the  cut 
faces.  Because  the  upper  surface  somewhat  resembles  the 
rough  cross-cut  section  of  a  compact  bundle  of  fibers, 
the  name  vertical  fiber  has  been  given  to  this  type  of 
brick. 


Vitrified  Shale  and  Clay  Brick  261 

302.  Rattler  Test,  (a)  The  only  test  limit  commonly 
specified  for  paving  brick  is  the  percentage  of  loss  by  abra- 
sion when  subjected  to  the  rattler  test.  This  test  has  been 
standardized  by  the  American  Society  for  Testing  Materials 
as  Standard  Test  C7-15.  Briefly  described,  the  standard 
rattler  consists  of  a  steel  barrel  made  up  of  two  solid  heads 
with  staves  spaced  T%  inch  apart.  This  barrel  is  made  to 
revolve  about  a  horizontal  axis  at  a  standard  rate  of  speed. 
The  abrasive  charge  consists  of  10  cast-iron  spheres,  weigh- 
ing 7J  pounds  each,  and  a  sufficient  number  of  smaller 
spheres,  weighing  0.95  pound  each,  to  bring  the  total  weight 
of  charge  to  as  near  300  pounds  as  possible.  The  brick 
charge  consists  of  10  thoroughly  dried  brick,  none  of  which 
would  be  rejected  upon  visual  inspection  and  which  are 
carefully  weighed.  The  test  consists  in  subjecting  the  brick 
to  1800  revolutions  of  the  rattler,  at  the  end  of  which  time 
they  are  re  weighed,  rejecting  any  fragment  weighing  less 
than  1  pound.  The  loss  in  weight  is  calculated  as  percen- 
tage of  the  original  weight  and  test  results  are  expressed  as 
per  cent  of  wear.  Sometimes  each  individual  brick  is  marked 
for  identification  by  drilled  holes,  weighed  separately,  and 
its  individual  per  cent  of  wear  determined. 

(6)  Specifications  covering  per  cent  loss  by  abrasion  of 
the  brick,  when  subjected  to  the  rattler  test,  vary  con- 
siderably. Sometimes  the  maximum  loss  of  the  entire 
charge  only  is  specified  and  sometimes  both  maximum  and 
minimum  loss  of  individual  brick  are  covered.  Occasionally 
the  loss  of  different  grades  of  brick-  obtained  from  different 
degrees  of  burning,  as  ascertained  by  visual  inspection,  is 
covered  in  specification  requirements.  Sampling  brick  for 
the  rattler  test  (§  306)  is  a  matter  which  may  require  con- 
siderable judgment  on  the  part  of  the  Inspector,  depending 
upon  specification  requirements.  Typical  specifications  of 
the  U.  S.  Bureau  of  Public  Roads  for  brick  of  4-inch  and 
3-inch  depth  include  the  following  requirements  in  connec- 
tion with  the  rattler  test: 


262 


Brick  and  Block  Pavements 


Rattler  loss 

4"  Brick 

3"  Brick 

Average  loss  on  one  or  more  rattler  charges,  not 
more  than  
Maximum  loss  by  any  one  charge  when  two  or  more 
samples  are  tested  

22% 
24% 

26% 

28% 

Maximum  difference  in  per  cent  of  loss  between  any 
two  charges       ..... 

8 

8 

It  is  further  specified  that  a  maximum  of  three  tests  may 
be  used  as  a  basis  for  rejection. 

303.  Size.  Although  there  are  exceptions,  the  size  of 
paving  brick  or  block  has  been  fairly  well  standardized 
within  reasonably  narrow  limits.  The  average  length  is 
8J  inches  and  width  3|  inches.  Two  depths  are  used,  4 
inches  and  3  inches.  Four-inch  brick  weigh  approximately 
10,000  pounds  per  thousand  and  three-inch  brick  about 
7,500  pounds  per  thousand.  The  weight  of  different  makes 
of  brick  of  a  given  size  may  vary  considerably,  however,  as 
their  specific  gravity  varies  from  1.9  to  2.7  with  an  average 
of  a  little  over  2.3.  Variation  in  the  width  and  depth  of 
individual  brick  from  a  single  plant  or  for  a  given  job  is 
usually  specified  at  not  over  f  inch  and  variations  in  length 
at  not  over  J  inch.  In  addition  to  such  limitations,  typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads  require 
brick  to  meet  the  following  dimension  limitations: 


Dimensions 

4"  Brick 

3"  Brick 

Length  in  inches 

8i-9£ 

8-9 

Width  in  inches    .... 

3f_3f 

31-4 

Depth  in  inches  

3|-4i 

2f-3t 

304.  Joints.  With  lug  brick  averaging  8J  inches  in 
length  and  3J  inches  in  width,  40  will  be  required  per  square 
yard.  The  joint  spaces  will  then  be  approximately  J  inch 
in  width  and  will  amount  to  106  square  inches  to  the  square 


Vitrified  Shale  and  Clay  Brick  263 

yard,  or  about  8  per  cent  of   the  total  area.     The  joint 
volume  for  a  4-inch  brick  pavement  will  then  approximate 


10 


15  20  25 

WIDTH  OF  PAVEMENT,  FEET 


35 


Fig.  36     Quantities  of  Materials  Required  for  Filling  Joints  in 
Brick  Pavements 

424  cubic  inches  and  for  a  3-inch  pavement  318  cubic  inches. 
This  volume  may  be  reduced  from  6  to  12  per  cent,  for  4- 


264  Brick  and  Block  Pavements 

inch  brick,  and  from,  8  to  16  per  cent  for  3-inch  brick,  by 
cushion  material  being  forced  up  into  the  joints  when  the 
brick  are  rolled.  With  all  of  these  factors  in  mind  and 
allowing  for  surface  wastage  or  cover,  Fig.  36  shows  the 
approximate  range  in  quantities  of  joint  filling  materials 
required  per  100  linear  feet  of  pavement  of  different  widths, 
when  constructed  of  4-inch  brick. 

These  values  should  be  multiplied  by  0.7  to  ascertain 
approximate  quantities  required  when  3-inch  brick  are  used. 
The  amounts  per  square  yard  may  be  ascertained  by  divid- 
ing the  values  for  nine-foot  width  by  100.  If  in  the  case  of 
bituminous  fillers,  it  is  desired  to  ascertain  the  number  of 
tons  required  reference  may  be  made  to  Fig.  7  for  the  pur- 
pose of  translating  the  values  in  gallons  to  tons. 

305.  Visual  Inspection,  (a)  Paving  brick  should  be  sub- 
jected to  careful  visual  inspection  in  order  to  cull  out  and 
reject  those  which  are  off  size  or  defective,  as  defined  by 
specifications.  In  addition  to  dimensional  limitations  (§'  303), 
specifications  eliminate  certain  defects.  Whether  or  not 
brick  have  been  inspected  at  the  plant,  they  should  again 
be  inspected  after  delivery,  at  place  of  use,  during  and  after 
la}dng  and  rolling.  Rejected  brick  should  be  culled  out 
and  promptly  removed  from  the  work.  Typical  specifica- 
tions of  the  U.  S.  Bureau  of  Public  Roads  cover  the  follow- 
ing points  which  are  subject  to  visual  inspection.  When 
broken  the  brick  shall  show  a  dense,  stone-like  body,  free 
from  lime,  air  pockets,  cracks  or  marked  laminations.  Kiln 
marks  shall  not  exceed  ^  inch  and  the  wearing  surface  shall 
show  but  slight  kiln  marks.  All  brick  shall  be  rejected 
which  are  broken  through  or  chipped  in  such  manner  that 
the  wearing  surface  does  not  remain  intact,  or  in  such 
manner  that  the  lower  surface  is  reduced  in  area  by  more 
than  one  eighth.  All  brick  shall  be  rejected  that  are  cracked 
to  a  depth  greater  than  f  inch  on  any  surface,  or  that  are 
cracked  on  the  wearing  surface.  All  brick  shall  be  rejected 
that  are  so  misshaped,  bent,  twisted,  or  kiln  marked  that 


Vitrified  Shale  and  Clay  Brick  265 

they  will  not  form  a  proper  surface  or  align  properly  with 
other  brick.  All  brick  shall  be  rejected  that  are  .obviously 
soft  or  poorly  vitrified. 

(6)  In  addition  to  inspecting  for  detection  of  defects,  the 
Inspector  should  see  that  other  specification  requirements 
such  as  size  and  form  are  met.  Some  of  these  points  are 
covered  by  typical  specifications  of  the  U.  S.  Bureau  of 
Public  Roads  as  follows:  "Only  brick  with  lugs  on  one 
side,  raised  not  less  than  f  inch  nor  more  than  J  inch  shall 
be  used.  The  ends  of  the  brick  shall  have  either  a  semi- 
circular groove,  with  a  radius  of  not  less  than  f  inch  or  more 
than  |  inch,  or  a  bulge  of  at  least  TV  inch.  The  name  or 
trade  mark  of  the  manufacturer,  if  shown  on  the  brick  shall 
be  recessed  and  not  raised.  If  the  edges  of  the  brick  are 
rounded,  the  radius  shall  not  exceed  T%  inch." 

306.  Sampling,  (a)  Samples  of  the  brick  for  the  rattler 
test  (§  302)  may  be  taken  at  the  point  of  manufacture  or 
from  cars  or  barges  at  the  point  of  delivery.  Each  sample 
should  consist  of  12  brick  and  should  be  packed  and  shipped 
in  a  stout  box  put  up  in  two  rows  of  6  brick  each,  separated 
by  a  wooden  partition.  No  single  sample  should  represent 
more  than  100,000  brick.  No  brick  should  be  included 
which  would  be  rejected  on  the  basis  of  cracks,  chips  or 
other  defects  covered  by  the  specification  clauses  for  visual 
inspection.  The  following  methods  for  sampling  were 
adopted  at  the  First  Conference  of  State  Highway  Testing 
Engineers  and  Chemists. 

(6)  Samples  from  the  plant  should  preferably  be  taken 
from  the  kiln  at  the  time  of  emptying.  One  or  more  sets 
of  samples,  each  set  consisting  of  three  samples  should  be 
taken  from  each  kiln,  depending  upon  its  size.  Each  sample 
in  a  set  should  then  represent  approximately  a  single  degree 
of  burning,  based  on  the  position  of  the  brick  in  the  kiln. 
Samples  taken  from  piles  at  the  plant  should  represent  as 
nearly  as  possible  the  entire  run  of  the  brick.  Samples 
should  be  taken  from  as  many  different  points,  correspond- 


266  Brick  and  Block  Pavements 

ing  to  the  length,  breadth  and  depth  of  the  pile  as  possible. 
In  no  case  should  samples  be  confined  to  the  upper  or  outer 
few  layers.  Where  controversy  arises  regarding  the  admis- 
sibility  of  certain  types  or  portions  of  the  lot,  entire  test 
samples  may  be  selected  from  such  types  or  portions  having 
a  characteristic  appearance  in  common. 

(c)  When  sampled  at  the  point  of  delivery  a  representa- 
tive sample  should  be  taken  from  each  carload  received. 
Considerations  covered  under  sampling  from  piles  at  the 
plant  apply  equally  to  sampling  from  cars. 

SLAG  BLOCK 

307.  Manufacture.     Slag    block,    commonly    known    as 
scoria   block,    are   manufactured   from   blast   furnace   slag 
(§  1686)  by  running  the  molten  slag  into  rectangular  molds 
where  they  are  allowed  to  slowly  cool  and  harden.    At  the 
present  time  few,  if  any,  slag  block  are  manufactured  in 
this  country  and  when  used  here  they  are  usually  imported 
from  England. 

308.  Properties.     Slag  block   are   of  approximately  the 
same  size  as  paving  brick  with  the  edges  on  the  upper  face 
slightly  beveled.    The  imported  variety  are  hard  and  dense 
and  have  a  higher  specific  gravity  than  brick.     They  are 
highly  resistant  to  the   destructive  action  of  heavy  traffic 
and  have  been  successfully  used  for  paving  between  street 
car  tracks,  to  which  purpose  their  use  in  this  country 'has 
been  generally  limited. 

STONE  BLOCK 

309.  Types  of  Block.     Stone  block  for  paving  purposes 
are  usually  manufactured  from  granite  (§  21)  or  sandstone 
(§  23)  although  trap  (§  20)  and  limestone  (§  22)  have  been 
used  to  a  very  limited  extent.     The  ordinary  size  of  block 
are  cut  or  split  by  hand  from  dimension  stone  or  larger  rec- 
tangular blocks  which  have  been  carefully  quarried.    For  this 


Stone  Block 


267 


purpose  the  rock  must  split  readily  along  two  planes  at  right 
angles  to  each  other.  Small  cubical  block  known  as  irregular 
sets  and  marketed  under  the  name  of  "Durax"  are  cut 
from  granite  by  a  machine  instead  of  by  hand. 

310.  Tests.     No  absolutely  satisfactory  set  of  tests  for 
stone  block  has  as  yet  been  devised  and  at  present  specifi- 
cation requirements  for  physical  properties  cover  only  resist- 
ance to  abrasion  (§  28)  and  toughness  (§  29)  as  determined 
upon  rock  used  in  the  manufacture  of  broken  stone.    At  one 
time  a  minimum  crushing  strength  was  commonly  specified 
but  it  is  now  generally  conceded  that  this  test  is  of  no  prac- 
tical  value  in   connection  with   paving  block.     The   1916 
specifications  of  the  American  Society  for  Municipal  Im- 
provements require  for  granite  block,  for  heavy  traffic,  a 
minimum  toughness  of  9  and  a  minimum  French  coefficient 
of  wear  of  11.    For  medium  traffic  a  minimum  toughness  of 
7  and  a  minimum  French  coefficient  of  wear  of  8  are  specified. 

311.  Size,     (a)  Stone   block  may  be    obtained    in    rec- 
tangular-shapes of  any  desired  dimensions.    Three  sizes  only 
of  granite  block  are,  however,  ordinarily  manufactured,  the 
dimension  limits  of  each  size  being  shown  in  the  following 
table.     Of  these  the  5-inch  standard  size  is  the  one  most  com- 
monly used.    Specifications  for  length  and  width-usually  men- 


Dimensions 

5-Inch 
Standard 

4-Inch 
Standard 

Resurfacing 

Length  in  inches                   .  • 

8  -12 

7-11 

7  -11 

Width  in  inches  
Depth  in  inches  

3f-4* 

4f-5i 

4-4£ 
4-4^ 

8f4I 

3£-4 

tion  the  top  surface  only,  but  they  frequently  require  that  the 
block  shall  be  so  dressed  that  when  laid  as  specified,  meas- 
urement of  any  joint  shall  show  a  width  of  not  more  than 
i  inch  for  a  depth  of  1  inch,  or  a  width  of  not  more  than  1 
inch  in  any  part  of  the  joint.  The  wearing  surface  of  the 
blocks  may  furthermore  be  required  to  show  no  depressions 


268  Brick  and  Block  Pavements 

more  than  f  inch  deep,  and  the  edges  and  corners  to  be 
unchipped  and  unbroken. 

(6)  "Durax"  block  or  cubes  are  ordinarily  specified  to 
have  six  irregular  but  approximately  square  surfaces,  the 
edges  of  which  measure  from  2f  to  4  inches  with  a  maxi- 
mum variation  of  not  more  than  f  inch  for  cubes  used  on 
any  one  city  block. 

312.  Joints.     For  a  standard  block  10  inches  long  and  4 
inches  wide  28.5  will  be  required  per  square  yard  with  an 
average  joint  of  f-inch  width.     The  joint  area  per  square 
yard  will  then  amount  to  156  square  inches  or  about  12 
per  cent  of  the  total  area.     The  joint  volume  per  square 
yard  for  a  5-inch  block  is  then  780  cubic  inches,  but  this 
may  be  reduced  from  10  to  20  per  cent  by  ramming  the 
block  into  the  cushion.     Upon  this  basis  and  allowing  for 
surface  wastage  or  cover,  Fig..  37  shows  the  approximate 
range  in  quantities  of  joint  filling  materials  required  per 
100  linear  feet  of  pavement  of  different  widths.    Quantities 
of  joint  filling  materials  for  the  smaller  sizes  of  stone  block, 
including  irregular  sets  of  Durax,   will  vary  considerably 
from  the  values  shown  in  this  diagram. 

The  amounts  per  square  yard  may  be  ascertained  'by 
dividing  the  values  for  nine-foot  width  by  100.  If  in  the 
case  of  bituminous  grout  it  is  desired  to  ascertain  the  num- 
ber of  tons  required,  reference  may  be  made  to  Fig.  7  for 
the  purpose  of  translating  the  values  in  gallons  of  bitumi- 
nous material  to  tons. 

313.  Visual  Inspection.     Stone  block  should  be  subjected 
to  careful  visual  inspection  in  order  to  cull  out  and  reject 
those  which  are  off  size  or  defective,  as  defined  by  specifica- 
tions.    Whether  or  not  they  have  been  inspected  at  the 
plant  they  should  again  be  inspected  after  delivery,  at  place 
of  use,  during  laying  and  after  ramming.     In  addition  to 
dimensional   limitations    (§311)    specifications   require    the 
block  to  possess  certain  qualities  and  to  be  free  from  defects. 
Thus,  the  kind  of  stone  may  be  specified  and  the  block  may 


Stone  Block 


269 


be  required  to  be  of  medium-sized  grain,  showing  an  even 
distribution  of  constituent  minerals.  They  should  be  of 
uniform  quality  and  texture  throughout,  and  free  from 
seams,  scales  or  disintegrated  material. 


10 


15 


-      S 


10 


15  20  25  30 

WIDTH  OF  PAVEMENT,  FEET 


Fig.  37     Quantities  of  Materials  Required  for  Filling  Joints  in 
Stone  Block  Pavements 


270  Brick  and  Block  Pavements 

*  „ 

314.  Sampling.     Stone  block  may  be  sampled  for  quality 
and  size  either  at  the  quarry  or  at  point  of  delivery.    A 
preliminary  sample  for  quality,  consisting  of  at  least  four 
blocks  of  common  size,  should  be  submitted  at  least  two 
weeks  prior  to  the  date  of  acceptance  or  rejection.     In  the 
case  of  irregular  sets  samples  should  be  taken  of  the  rock 
as  previously  described  (§  39) .    Additional  samples  of  block 
may  be  taken  from  time  to  time  during  the  progress  of  the 
work,  whenever  the  quality  or  appearance  of  the  blocks 
varies,  and  at  such  other  times  as  may  be  directed  by  the 
Engineer.     No  samples  should  include  block  which  would 
be  rejected  on  visual  inspection.     Preliminary  samples  are 
sometimes  omitted  in  cases  where  material,  from  the  pro- 
posed source  of  supply,  has  been  tested  within  one  year 
prior  to  the  date  of  acceptance  or  rejection,  if  the  source 
of  supply  is  a  large  quarry  in  connection  with  which  previous 
tests  have  shown  a  uniform  and  satisfactory  output.     In 
this  case  the  report  of  such  tests  may  be  used  as  a  basis  of 
acceptance   or  rejection.     Samples  of  stone  block  should 
be  shipped  in  stout  boxes  or  crates. 

ASPHALT  BLOCK 

315.  Manufacture  and  Composition,     (a)  Asphalt  block 
are  manufactured  from  a  fine  aggregate  asphaltic  concrete 
by  compressing  the  hot  mix  in  molds  by  means  of  an  hy- 
draulic press,  so  that  each  block  is  subjected  to  a  pressure 
of  from  200  to  300  tons.    The  blocks  are  then  forced  from 
the  molds,  measured  for  thickness  and  cooled  by  passing 
them,  on  a  conveyor  belt,  under  water.     The  process  of 
heating  and  combining  the  constituents  of  the  mix  is  prac- 
tically identical  with  ordinary  paving  plant  practice  (§§  239- 
243)   and  is  subject  to  the  same  kind  of  inspection.    The 
mineral  aggregate  ordinarily  consists  of  crushed  trap  rock, 
all  of  which  will  pass  a  i-inch  screen,  and  limestone  or  dolo- 
mite dust.     Limestone  is  also  used  to  some  extent  for  the 


Asphalt  Block  271 

coarser  part  of  the  aggregate.  The  asphalt  cement  is  similar 
to  that  used  in  sheet  asphalt  construction-  but  usually 
harder  or  of  lower  penetration  (§  280). 

(6)  Specifications  for  asphalt  block  sometimes  limit  the 
type  and  grading  of  the  mineral  aggregate  as  well  as  the 
physical  and  chemical  properties  of  the  asphalt  cement  in 
the  same  manner  as  for  any  other  bituminous  concrete.  In 
such  cases  plant  inspection  is  required  both  in  connection 
with  the  materials  used  and  the  methods  of  combining  them 
and  compressing  the  block.  Other  specifications  rely  upon 
requirements  which  the  block  themselves  must  meet  when 
subjected  to  test. 

316.  Tests.     The  usual  tests  specified  in  connection  with 
the  manufactured  block  are  specific  gravity  (§  383),  absorp- 
tion (§  382),  per  cent  of  bitumen  (§  133)  and  grading  of  'the 
mineral  aggregate  (§  371).     As  an  illustration  the  following 
requirements  are  cited  from  the  1917  specifications  of  the 
New  York  State  Highway  Commission. 

Specific  Gravity:  Per  cent 

Trap  rock  blocks,  not  less  than 2.45 

Limestone  blocks,  not  less  than 2.30 

Absorption  when  immersed  in  water  for  seven  days: 

Not  more  than 0.75 

Bitumen  (soluble  in  carbon  disulphide) 6.5-8.5 

Mineral  Aggregate:  Per  cent 

Passing  J-inch  screen 100 

"        10-mesh,  retained  on  20-mesh  sieve 15-20 

"       20-    "  "         "  40-    "        "    8-16 

"       40-    "  "         "  80-    "        "    8-14 

«       80-    "  "         "  200-  "        "     12-18 

"     200-     "      not  less  than 18 

317.  Size.     Asphalt  paving  block  are  usually  manufac- 
tured 12  inches  in  length  and  5  inches  in  width.     Three 


272  Brick  and  Block  Pavements 

standard  depths  are  used,  2,  2|  and  3  inches.  Specifications 
for  size  usually  allow  a  tolerance  of  J  inch  in  length  and  J 
inch  in  width  and  depth,  from  specified  dimensions.  As 
good  block  are  smooth  and  regular  they  may  be  set  very 
close  together  so  as  to  produce  but  little  joint  space.  A 
cover  of  sand  spread  J  of  an  inch  thick  should  be  more  than 
sufficient  to  fill  all  voids  in  a  three-inch  block  pavement  and 
less  may  ordinarily  be  used.  On  heavy  grades  and  under 
heavy  traffic  conditions,  the  use  of  anchor  blocks  is  some- 
times specified.  Such  blocks  are  of  the  same  size  and  shape 
as  the  ordinary  block  but  have  a  steel  form,  of  special  shape, 
imbedded  in  their  lower  surface  so  as  to  project  about  one- 
half  inch  into  the  mortal*  cushion  on  which  they  are  laid. 
At  suitable  intervals  a  row  of  anchor  blocks  is  laid  across 
the*  pavement  to  prevent  undue  movement  in  the  adjoining 
areas. 

318.  Inspection  and  Sampling,  (a)  Depending  upon  spe- 
cification requirements,  the  inspection  of  asphalt  block  pave- 
ments may  involve  the  services  of  a  plant  Inspector  as  well 
as  a  street  Inspector,  as  in  the  case  of  bituminous  concrete. 
The  duties  of  an  asphalt  block  plant  Inspector  are  in  every 
way  similar  to  those  of  the  paving  plant  Inspector  except 
that  in  addition  to  the  regular  duties  of  the  former  he  may 
be  required  to  make  determinations  of  specific  gravity  (§  383) 
and  absorption  (§  382) .  Both  plant  and  street  Inspector 
should  subject  each  shipment  of  block  to  careful  visual 
inspection,  in  order  to  cull  out  any  which  are  off  size  (§  317) 
or  defective  under  specification  requirements.  All  block 
should  be  uniform  in  texture  and  shape,  with  parallel  faces, 
free  from  warp,  checks  or  cracks.  The  edges  should  be 
straight,  sharp  and  .unchipped  and  the  corners  unbroken. 

(6)  One  sample  consisting  of  two  block  should  be  taken 
from  every  car  load  received  unless  the  block  have  been 
inspected  and  sampled  at  the  plant,  in  which  case  at  least 
one  sample  should  be  taken  from  every  100,000  block  or 
less.  Sample  blocks  should  be  free  from  all  defects  which 


Wood  Block  273 

would  prevent  their  passing  visual  inspection.  Samples 
should  be  carefully  packed  'and  shipped  in  stout  wooden 
boxes. 

WOOD  BLOCK 

319.  Manufacture.  Wood  paving  block  are  manufac- 
tured from  a  variety  of  woods  such  as  long-leaf  yellow 
pine,  Douglas  fir,  tamarack,  Norway  pine,  hemlock  and 
black  gum.  The  first  mentioned  wood  has  probably  been 
used  to  the  greatest  extent  and  is  ordinarily  preferred  al- 
though specifications  usually  allow  a  variety  of  woods  to 
compete.  As  the  blocks  are  laid  with  the  end  of  the  grain 
up,  long  planks  are  first  sawed  and  surfaced  to  suitable 
width  and  thickness  so  that  when  cut  the  cross  section  will 
give  the  length  and  width  of  blocks  which  are  desired.  The 
block  are  formed  by  sawing  the  plank  into  such  sections  as 
will  produce  the  desired  depth  of  block.  In  the  ordinary 
plant  the  block  are  then  loosely  and  irregularly  stacked  in 
metal  cages,  carried  on  narrow  gauge  cars,  and  are  run  into 
long  horizontal  iron  cylinders  which  are  then  closed  tight 
at  both  ends.  These  are  known  as  treating  or  creosoting 
tanks  and  are  equipped  with  steam  coils.  Vertical  tanks  are 
used  to  a  limited  extent,  in  which  case  the  block  are  carried  to 
the  tank  directly  from  the  saw  by  means  of  disc  conveyors. 

(6)  Various  methods  of  preliminary  treatment  are  given 
the  block  before  they  are  impregnated  with  creosoting  oil 
but  in  general  the  process  is  as  follows:  After  the  block 
have  been  placed  in  the  tank,  which  is  then  tightly  closed 
they  are  subjected  to  the  action  of  I've  steam  at  104°  to 
116°  C.  for  from  2  to  4  hours  after  which  the  steam  is 
exhausted  and  a  vacuum  of  not  less  than  22  inches  is  main- 
tained for  at  least  1  hour.  At  the  end  of  the  vacuum  treat- 
ment and  while  the  vacuum  is  still  on,  creosoting  oil  is  run 
into  the  tank,  until  the  cylinder  is  completely  filled,  and 
heated  to  a  temperature  of  from  84°  to  104°  C.  Additional 
oil  is  then  forced  in  until  pressure  is  gradually  developed, 
not  to  exceed  50  pounds  per  square  inch  at  the  end  of  the 


274  Brick  and  Block  Pavements 

first  hour  nor  100  pounds  at  the  end  of  the  second  hour. 
Finally,  a  pressure  of  from  100  to  150  pounds  per  square 
inch  is  maintained  until  the  required  amount  of  oil,  usually 
from  16  to  20  pounds  per  cubic  foot,  has  been  absorbed  by 
the  block.  The  oil  is  then  run  out  of  the  tank  and  a  vacuum 
of  at  least  20  inches  is  applied  for  not  less  than  30  minutes. 
This  is  sometimes  followed  by  a  short  steaming  process 
after  which  the  treated  block  are  discharged  from  the 
tank. 

(c)  The  first  steam  treatment  of  the  block  serves  two  pur- 
poses: first,  to  heat  the  block  so  as  to  receive  the  oil  without 
chilling  it;  second,  to  regulate  the  moisture  content  of  the 
wood  which,  as  charged  into  the  tank,  may  be  either  too 
dry  or  too  wet.  The  vacuum  treatment  serves  to  remove 
air  and  excess  moisture  from  the  wood  cells  so  that  the  oil 
will  be  properly  absorbed. 

320.  Requirements,  (a)  No  reliable  tests  for  creosoted 
wood  block  have  as  yet  been  devised  and,  in  order  to 
secure  a  satisfactory  product,  specifications  usually  contain 
rather  rigid  requirements  relative  to  manufacture,  which 
necessitate  the  services  of  a  plant  Inspector  (§  323) .  As  an 
example,  the  method  of  treatment  just  described  (§  3196) 
is  included  in  the  1916  specifications  of  the  American  So- 
ciety for  Municipal  Improvements. 

(6)  In  addition  to  listing  the  types  of  wood  allowed,  only 
one  of  which  should  be  used  in  any  given  contract,  these 
specifications  require  that  the  blocks  must  be  sound,  square 
butted,  square  edged,  free  from  unsound,  loose  or  hollow 
knots,  knot  holes  and  other  defects  such  as  shakes,  checks, 
etc.,  that  would  be  detrimental  to  the  block.  The  number 
of  annual  rings  in  the  1  inch  which  begins  2  inches  from 
the  pith  of  the  block  is  specified  at  not  less  than  6,  meas- 
ured radially,  provided,  however,  that  blocks  containing 
between  5  and  6  rings  in  this  inch  shall  be  accepted  if  they 
contain  33.3  per  cent  or  more  summer  wood.  In  case  the 
block  does  not  contain  the  pith,  the  1  inch  to  be  used  should 


Wood  Block  275 

begin  1  inch  away  from  the  ring  which  is  nearest  to  the 
heart  of  the  block.  It  is  further  specified  that  the  blocks  in 
each  charge  shall  contain  an  average  of  at  least  70  per  cent 
of  heartwood  and  that  no  one  block  shall  be  accepted  that 
contains  less  than  50  per  cent  of  heartwood. 

(c)  Specifications  for  size  of  wood  block  vary  considerably 
but,  in  general,  they  run  from  5  to  10  inches  in  length  and 
from  3  to  4  inches  in  width.     The  depth  should  preferably 
be  one-half  of  the  length  and  at  least  J  of  an  inch  greater  or 
less  than  the  width.     Between  individual  block  a  variation  of 
1*5-  inch  in  depth  and  f  inch  in  width  from  the  dimensions 
specified  is  usually  allowed.     For  heavy  traffic,   block  4 
inches  in  depth  are  commonly  used  and  for  moderate  traffic, 
3|  inches. 

(d)  Requirements  for  creosoting  oils   (§  105)   have  been 
fairly  well  standardized  by  the  1916  specifications  of  the 
American  Society  for  Municipal  Improvements  and  by  Ten- 
tative Standard  D52-18T  of  the  American  Society  for  Test- 
ing Materials.     Both  of  these  specifications  require  the  use 
of  either  a  coal-tar  paving  oil  or  a  distillate  oil  although  an 
additional   specification   for  water-gas  tar  is  also  included. 
Limits  of  physical  and  chemical  properties  of  these  three 
types  of  preservatives  as  determined  by  laboratory  tests 
are  shown  under  Typical  Material  Requirements   (§  414). 
A  number  of  the  requirements  serve  the  purpose  of  identi- 
fication only.     The  direct  suitability  requirements  limit  the 
amount   of  water    and   free    carbon   or    insoluble   material 
which  tends  to  prevent  proper  absorption  by  the  block,  and 
also  the  presence  of  an  undue   amount  of  readily  volatile 
constituents. 

321.  Joints.  Wood  block  are  ordinarily  set  close  to- 
gether in  the  pavement  so  that  joints  do  not  exceed  J  inch 
in  width,  except  in  the  case  of  lug  blocks  when  the  joint  is 
about  i  inch.  The  joint  space  per  square  yard  will,  of  course, 
vary  with  the  size  of  block  used  (§  320c).  Allowing  J-inch 
joints  between  blocks  8J  inches  long,  4  inches  wide  and 


276 


Brick  and  Block  Pavements 


4J  inches  deep,  about  36.5  will  be  required  per  square  yard, 
the  joint  area  being  4.4  per  cent,  and  the  joint  volume  278 
cubic  inches  per  square  yard.  If  the  cushion  material  is 
assumed  to  occupy  \  inch  of  depth,  the  joint  volume  is  262 
cubic  inches  per  square  yard.  Upon  this  basis  and  allowing 


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Fig.  38     Quantities  of  Materials  Required  for  Filling  Joints  in 
Wood  Block  Pavements 

i  iiuwjifUB  .•.')!•:  'iu  ti'Mioacnq  ^ri.t  «>*5;b> 

for  surface  wastage  or  excess,  Fig.  38  shows  the  approximate 
number  of  gallons  of  bituminous  material  required  to  fill 
100  linear  feet  of  pavement  of  different  widths  and  also  the 
amount  of  sand  cover  required.  The  amounts  of  bituminous 
material  and  sand  required  per  square  yard  may  be  ascer- 
tained by  dividing  the  values  for  nine-foot  width  by  100.  If 
it  is  desired  to  ascertain  the  number  of  tons  required  refer- 


Wood  Block  277 

ence  may  be  made  to  Fig.  7  for  the  purpose  of  translating  the 
values  in  gallons  to  tons. 

322.  Inspection,  (a)  Wood  block  should  be  subjected 
to  visual  inspection  both  at  the,  plant,  and  after  delivery  at 
place  of  use,  during  and  after  laying  and  rolling,  in  order 
to  cull  out  and  reject  those  which  are  off  size  or  defective 
under  specification  requirements  (§  320) .  Blocks  should  be 
laid  as  soon  after  treatment  as  possible.  Specifications  of 
the  American  Society  for  Municipal  Improvement,  adopted 
in  1916,  require  that  if  they  cannot  be  laid  within  2  days, 
provision  should  be  made  to  prevent  them  from  drying  out, 
by  stacking  them  in  close  piles  under  cover,  and  sprinkling 
them  thoroughly  with  water  at  intervals.  They  should  be 
thoroughly  sprinkled  about  two  days  before  laying. 

(&)  Plant  inspection  not.  only  involves  visual  examina- 
tion of  the  finished  block,  as  covered  in  the  preceding  para- 
graph,'but  also  inspection  of  the  untreated  wood  and  the 
details  of  manufacture  included  in  specification  require- 
ments. This  may  necessitate  certain  tests  in  connection 
with  plant  operation  (§  323).  Culling  of  the  finished  block 
will  be  considerably  reduced  by  inspecting  the  planks  before 
they  are  sawed,  so  as  to  reject  those  which  would  produce 
blocks  that  could  not  meet  the  specifications.  It  is  also 
advisable  to  sort  acceptable  plank,  so  as  to  obtain  for  any 
one  charge  of  block,  lumber  of  approximately  uniform  weight 
per  cubic  foot.  This  is  indicated  by  the  spacing  and  tex- 
ture of  the  annual  rings  as  shown  by  the  end  sections  of  the 
plank.  Each  annual  ring  is  composed  of  a  dense  area, 
caused  by  slow  winter  growth,  and  a  lighter  and  more 
porous  area  of  relatively  rapid  summer  growth  wood.  In 
connection  with  treatment,  records  should  be  kept  of  the 
number  of  cubic  feet  of  wood  in  each  charge,  the  weight  of 
oil  absorbed  by  each  charge  as  determined  from  tank  read- 
ings, and  of  the  temperature,  time  and  pressure  of  each  phase 
of  treatment,  as  determined  by  thermometers  and  gauges 
which  are  a  part  of  the  plant  equipment.  The  volume  of 


278  Brick  and  Block  Pavements 

oil  forced  into  the  wood  is  indicated  by  the  difference  in 
level  of  oil  in  the  storage  tank  between  the  time  that  pres- 
sure is  applied  and  when  the  pressure  is  released.  The 
weight  of  oil  absorbed  is  th^n  ascertained  from  its  specific 
gravity  (Fig.  7)  as  determined  by  laboratory  test  (§  121). 
The  weight  of  oil  per  cubic  foot  of  wood  is  calculated  by 
dividing  the  total  weight  of  oil  absorbed  by  the  number  of 
cubic  feet  of  wood  in  the  charge.  As  a  check  upon  such 
measurements  and  calculations  the  Inspector  should  occa- 
sionally make  a  test  upon  a  cubic  foot  sample  of  block  which 
is  suspended  in  a  wire  cage  in  the  treating  tank  throughout 
the  entire  treatment.  The  difference  in  weight  of  sample 
before  and  after  treatment  indicates  the  weight  of  oil  ab- 
sorbed per  cubic  foot.  In  this  test  (§  381)  the  amount  of 
moisture  in  both  the  untreated  and  treated  block  should  be 
taken  into  account  as  treatment  may  either  remove  or  add 
to  the  total  moisture  content. 

(c)  In  addition  to  ascertaining  the  amount  of  oil  absorbed 
by  the  block,  the  plant  Inspector  should  determine  whether 
or  not  satisfactory  penetration  and  diffusion  has  been  se- 
cured. To  determine  this,  at  least  25  block  should  be  taken 
from  different  parts  of  each  charge  and  sawed  in  half  at 
right  angles  to  the  fiber.  Specifications  of  the  American 
Society  for  Municipal  Improvement  require  that  the  oil 
must  be  diffused  throughout  the  sapwood  and  if  more  than 
one  of  the  25  blocks  show  untreated  sapwood,  the  charge 
shall  be  retreated.  It  is  further  specified  that  the  surface 
of  blocks  after  treatment  shall  be  free  from  deposit  of  ob- 
jectionable substances. 

323.  Sampling,  (a)  Except  for  his  own  tests  to  deter- 
mine weight  of  oil  absorbed  per  cubic  foot  of  wood  (§381) 
and  diffusion  of  the  oil  (§  322c)  the  plant  inspector  is  re- 
quired to  sample  only  the  preservative  oil,  which  should  be 
subjected  to  laboratory  tests  before  use.  The  following 
methods  for  sampling  creosote  oil  has  been  adopted  by  the 
American  Society  for  Testing  Materials,  under  Standard 


Wood  Block  279 

Method  D38-18,  in  cases  where  the  oil  is  being  loaded  or 
discharged  by  means  of  a  pump.  "A  J-inch  sampling  pipe 
should  be  inserted  in  the  line  through  which  the  oil  is  being 
pumped,  on  the  discharge  side  of  the  pump,  preferably  in 
a  rising  section  of  the  pipe  line.  This  sampling  pipe  shall 
extend  one  halfway  to  the  center  of  the  main  pipe  and 
with  the  inner  opening  end  of  the  sampling  pipe  turned  at 
an  angle  of  90  degrees  and  facing  the  flow  of  the  liquid.  This 
pipe  shall  be  provided  with  a  plug  cock  and  shall  discharge 
into  a  receiver  of  50  to  100  gallons  capacity.  The  plug  cock 
shall  be  so  adjusted  that,  with  a  steady  continuous  flow  of 
the  oil,  the  receiver  shall  be  filled  in  the  time  required  to 
pump  the  entire  shipment.  The  receiver  shall  be  provided 
with  a  steam  coil  sufficient  to  keep  the  contents  at  a  tem- 
perature not  exceeding  120°  F.  Immediately  upon  com- 
pletion of  the  pumping,  the  contents  of  the  receiver  shall 
be  very  thoroughly  agitated  and  a  duplicate  one-quart 
sample  taken  immediately  for  the  test.  The  amount  of 
the  drip  sample  collected  shall  not  be  less  than  one  gallon 
for  each  1000  gallons  of  oil  handled,  except  in.  the  case  of 
large  boat  shipments,  where  a  maximum  of  100  gallons  is 
sufficient." 

(6)  In  the  1916  specifications  of  the  American  Society  for 
Municipal  Improvements  the  following  method  of  taking 
storage  tank  samples  is  specified.  "In  sampling  from 
storage  it  is  necessary  to  secure  samples  from  different 
levels,  and  where  possible  this  may  be  done  by  means  of 
small  outlet  cocks,  at  regular  intervals,  from  the  top  to  the 
bottom  of  the  storage  tank.  In  such  cases  about  one  gallon 
of  tar  or  oil  shall  be  drawn  from  each  outlet  cock  and  thor- 
oughly mixed  and  a  portion  taken  for  testing.  The  stream 
from  each  cock  shall  always  be  allowed  to  flow  for  sufficient 
length  of  time  to  enter  the  outlet  pipe  and  nipple  before 
commencing  to  collect  the  sample.  When  tanks  have  no 
outlet  cocks,  a  vessel  having  a  string  attached  to  the  cork 
may  be  lowered  to  measured  depth,  representing  a  number 


280  Brick  and  Block  Pavements 

of  different  levels  in  the  tank,  and  the  cork  removed  when 
the  vessel  has  reached  the  proper  level.  These  samples 
shall  be  combined  for  an  average  as  above." 


MAINTENANCE 

324.  Methods,  (a)  Maintenance  of  brick  or  block 
pavements  may  involve  repairs  to  joint  filler  or  cracks, 
replacement  of  individual  block  or  areas  of  block,  surface 
treatment  with  bituminous  material,  or  sometimes  entire  re- 
laying with  most  of  the  block  originally  used  in  the  pavement. 

(b)  Failures  of  cement  grout  filler  in  limited  areas  may  be 
repaired  by  carefully  chipping  out  the  grout  for  a  depth  of 
not  less  than  J  inch,  carefully  cleaning  the  joints,  drench- 
ing them  with  water  and  applying  new  grout  as  in  original 
construction.     Extensive  failures  are  tedious  and  difficult 
to  repair,  but  after  thorough  cleaning  a  bituminous  surface 
treatment  may  improve  conditions.     Wear  of  bituminous 
joints  is  more  easily  remedied  by  reapplication  of  the  bitu- 
minous filler,  so  as  to  bring  the  joints  flush  with  the  adjacent 
pavement. 

(c)  Failure  of  individual  block  or  a  number  of  adjacent 
block  may  require  replacement,  in  which  case  the  defective 
block  should  be  carefully  removed  so  as  to  disturb  as  little 
as  possible  the  surrounding  area.     A  stone  chisel  should  be 
used  to  cut  out  cement  grout  joints  at  such  places.    Replace- 
ments should  be  made  only  with  whole  block  so  as  to  form 
a  dovetailed  patch  when  a  number  of  block  are  involved. 
The  new  block  should  be  laid  exactly  as  in  original  con- 
struction and  the  cushion  or  bed  adjusted  so  that  their 
upper  surface  is  brought  flush  with  the  surrounding  area. 

(d)  Cracks  in   cement-grouted  brick  pavements  may  be 
repaired  with  bituminous  material   as  described   for   con- 
crete pavements  (§  231a). 

(e)  Areas   which   have   heaved,    because    of   swelling   or 
expansion,  require  relaying  with  the  use  of  a  bituminous 


Maintenance  281 

filler  or  the  insertion  of  expansion  joints  at  proper  intervals. 
If  the  old  block  are  to  be  replaced  they  should  first  be  care- 
fully cleaned  and  culled,  to  reject  chipped,  broken  or  inferior 
block. 

(/)  When  a  pavement  through  long  hard  service  has 
worn  unevenly  and  the  surface  is  rough,  treatment  with 
cut-back  asphalt  or  tar  is  made  so  that  with  the  application 
of  cover  a  bituminous  mat  is  produced.  Sometimes  the  old 
pavement  is  made  to  serve  as  a  foundation  for  another  type 
of  pavement.  Occasionally  the  old  pavement  is  torn  up  and 
the  blocks  cleaned,  sorted  to  lots  of  uniform  thickness  and 
relaid  bottom  side  up.  In  the  case  of  old  granite  block  pave- 
ments, the  block  are  often  recut  by  breaking  them  in  half 
and  dressing  the  broken  surfaces.  The  cut  block  are  then 
relaid  with  the  fresh  cut  surface  up. 

325.  Inspection.     Inspection  of  maintenance  will  usually 
be  the  same  as  for  joint  filling  (§§  328-330),  surface  treat- 
ment (Chapter  IX)  or  original  construction.    The  extent  of 
sampling  will  depend  upon  the  amount  of  work  and  ma- 
terial involved. 

INSPECTOR'S  EQUIPMENT 

326.  Construction.     The  street  Inspector  may  require  the 
following  equipment  for  the  inspection  of  brick  and  block 
pavement. 

For  Measurements: 

A  50-foot  steel  tape. 

A  pocket  rule.  (§387). 

A  straight  edge  (§  357). 
For  Sampling; 

A  supply  of  close-woven  bags  for  grouting  sand. 

A  ball  of  stout  twine. 

A  supply  of  eyelet  tags  for  identification  information. 

A  supply  of  1  quart  tin  cans  with  tight  fitting  covers  for 
sampling  cement  or  bituminous  materials. 


282  Brick  and  Block  Pavements 

A  supply  of  gum  labels. 

A  few  stout  boxes  may  be   required   occasionally  for 
shipping  samples  of  block. 

For  Testing: 

A  thermometer  (§  386)  if  bituminous  filler  is  used. 

A  set  of  field  screens  and  sieves  with  suitable  openings 

as  may  be  covered  in  specifications  for  cushion  or 

grouting  sand  (§371). 
A  spring  balance  with  pan  capacity  of  200  grams  (§  371). 

For  Records  and  Reports: 
A  field  diary  and  pencil. 
A  supply  of  report  forms  (§  404) . 
A  carbon  paper  for  duplication  of  reports. 

In  addition  to  the  above  the  plant  Inspector  for  asphalt 
block  may  need  any  or  all  of  the  equipment  of  a  paving 
plant  Inspector  (§253).  For  wood  block  he  will  need,  in 
addition  to  the  above,  a  complete  test  outfit  for  determining 
the  weight  of  oil  per  cubic  foot  of  wood  (§  381) .  For  samples 
of  block  to  be  shipped  to  the  laboratory  a  number  of  stout 
wooden  boxes  or  crates  will  be  required. 

327.  Maintenance.  For  extensive  replacements,  the  In- 
spector's equipment  will  be  the  same  as  for  construction. 
For  maintenance  with  bituminous  materials,  it  will  be  the 
same  as  for  surface  treatment  (§  191). 


' 

' 


CHAPTER  XV 

INSPECTION  OF  MISCELLANEOUS 
WORK  AND   MATERIALS 

BITUMINOUS  EXPANSION   JOINTS 

328.  General  Characteristics.     In  highway  construction 
expansion  joints  are  usually  filled  with  bituminous  material 
which  will  compress  or  yield  as  the  joint  tends  to  close  with 
expansion  of  the  surrounding  pavement  and  thus  relieve  it 
of  compressive  strains  which  might  otherwise  crush  the  pav- 
ing material  or  cause  it  to  bulge  or  heave.    The  filler  should 
preferably  adhere  firmly  to  the  sides  of  the  joints,  so  that 
when   contraction   occurs  it  will  stretch  as  the  joint  opens 
and  thus,  keep  the   joint  water-tight.     Expansion    is  ordi- 
narily caused  by  heat  and  absorption  of  water,  while  con- 
traction is  caused  by  cold  and  drying  out.     Longitudinal 
joints  are  usually  placed  at  the  junction  of  pavement  with 
curb  or  gutter  and  are  not  subjected  to  as.  severe  traffic 
conditions  as  transverse  joints.     The  latter,  in  particular, 
should   be   carefully  maintained  by  the   addition   of  new 
filler  as  the  old  is  worn  away  or  disintegrated.    Each  joint 
in  a  bituminous-filled  brick  or  block  pavement  serves  as  an 
expansion  joint  and  sometimes,  in  an  otherwise  monolithic 
structure,  two  or  more  courses  of   bituminous-filled   block 
are  inserted  at  intervals  in  the  pavement  in  place  of  the 
usual  single  joint.    There  are  two  types  of  fillers,  known  as 
poured  joint  and  prepared  joint  fillers. 

329.  Poured    Joints,     (a)  Blown   asphalt    (§  97)    or   tar 
pitch  (§  104)  is  ordinarily  used  for  filling  joints  by  the  pour- 
ing method.     The  joint  space  is  formed  by  means  of  strips 

283 


284       Miscellaneous  Work  and  Materials 

of  wood  or  metal  of  suitable  thickness  which  are  inserted 
during  construction  and  later  withdrawn,  thus  leaving 
empty  slots.  Care  should  be  taken  that  these  slots  are 
kept  perfectly  clean  until  the  filler  is  poured  in.  Accumula- 
tions of  dirt,  sand  or  pebbles  in  the  slots  will  not  only  inter- 
fere with  properly  filling  the  joints  but  may  pack  so  as 
to  interfere  with  expansion  of  the  pavement.  The  bitu- 
minous material  is  usually  heated  in  kettles,  transferred  to 
hand  pouring  cans  with  narrow  spouts  or  outlets,  which 
may  be  inserted  in  the  top  of  the  joint  spaces,  and  allowed 
to  flow  into  the  joints  until  a  little  more  than  flush  with  the 
surrounding  surface.  A  slight  surplus  of  hot  material  is 
necessary  in  order  to  allow  for  shrinkage  upon  cooling.  The 
finished  joint  should,  however,  be  brought  practically  flush 
with  the  pavement  and  a  hot  smoothing  iron  may  be  used 
for  this  purpose  in  case  the  joint  is  overfilled.  It  is  impor- 
tant that  the  filler  be  heated  sufficiently  to  prevent  its 
chilling  too  rapidly  upon  contact  with  the  pavement,  but 
care  should  be  exercised  that  it  is  not  injured  by  overheating. 
Ordinarily  asphalt  fillers  should  not  be  heated,  to  over 
400°  F.  or  tar  fillers  to  over  325°  F.  At  least  one  sample  of 
filler  should  be  taken  from  every  shipment  received  (§  115). 
The  chemical  and  physical  properties  of  asphalt  and  tar 
filler  as  determined  by  laboratory  tests,  which  are  com- 
monly covered  by  specifications,  are  shown  under  Typical 
Material  Requirements  (§§411,  413). 

(6)  The  gallons  of  bituminous  material  needed  in  filling 
joints  is  ascertained  by  dividing  the  number  of  cubic  inches 
of  joint  space  by  231.  If  it  is  desired  to  ascertain  the  num- 
ber of  tons  of  filler,  the  cubic  inches  of  joint  space  should 
be  multiplied  by  the  specific  gravity  of  the  material  and  the 
resulting  product  multiplied  by  0.0000181. 

330.  Prepared  Joints.  Prepared  joint  fillers  (§§  97,  104) 
are  manufactured  in  strips  of  the  thickness  which  is  desired 
for  the  width  of  joint.  These  strips  are  sometimes  wider 
than  the  depth  of  the  joint  if  a  composition  is  used  which 


Paving  Adjacent  to  Car  Tracks          285 

contains  no  fabric.  Such  fillers  are  placed  during  construc- 
tion of  the  pavement  and  if  they  project  above  the  surface 
are  eventually  flattened  out  with  a  hot  smoothing  iron, 
which  not  only  brings  them  flush  with  the  surrounding 
pavement  but  seals  the  top  of  the  joint  and  renders  it  water- 
proof. If  the  filler  projects  more  than  f  inch  above  the  sur- 
face it  should  be  trimmed.  A  hot  shovel,  to  the  bottom  of- 
which  metal  cleats  have  been  riveted,  is  sometimes  used  for 
trimming  joints.  Prepared  joint  fillers  should  be  sampled 
as  previously  described  (§  117). 


PAVING  ADJACENT  TO   CAR  TRACKS 

331.  Materials.     Adjacent   to,    and   between,  street   car 
tracks,  brick  or  block  are  frequently  laid  irrespective  of  the 
paving  material  proper.    This  is  ordinarily  considered  good 
practice,   especially  in  the  case  of  bituminous  pavements, 
unless  the  track  construction  is  so  rigid  that  vibration  is 
reduced  to  a  minimum.     When  very  rigid   the  pavement 
proper   may   be    carried    to    the   rail.      Even   then   many 
engineers  consider  that  brick  or  block  should  preferably  be 
laid  between  all  rails  if  the  tracks  run  along  the  center  of 
the  pavement.    Special  forms  of  brick  or  block,  known  as  rail 
block,  are  frequently  used  directly  against  the  rail.     These 
block  are  designed   to  produce   a  close  smooth  joint  with 
rail,  so  constructed  or  set  that  a  perfectly  rectangular  block 
would  produce  a  poor  joint. 

332.  Methods.     Between  the  pavement  proper  and  the 
rail,  brick  are  often  set  for  a  width  of  18  inches  or  more  so 
as  to  extend  beyond  the  ties.     They  are  laid  upon  a  con- 
crete base  and  may  be  filled  with  cement  grout  or  bitumi- 
nous material.    Cement  mortar  or  bituminous  mastic  is  used 
as  a  filler  between  the  web  and  lip  of  the  rail  so  as  to  give 
the  adjacent  block  a  firm  setting.    Between  pavement  and 
rail  three  or  more  courses  of  block  may  be  laid  longitudi- 
nally, while  between  the  rails  the  courses  are  laid  trans- 


286       Miscellaneous  Work  and  Materials 

versely.  If  a  bituminous  pavement  is  carried  directly 
against  the  rail,  it  is  usually  laid  slightly  higher  than  the 
rail.  Especial  attention  should  be  paid  to  obtaining  as  tight 
a  rail  joint  as  possible  so  as  to  prevent  the  entrance  of  water. 


COLD  PATCHING 

333.  Materials.     So-called  cold  patching  has  become  a 
rather  popular  method  of  repairing  holes  and  depressions 
in  bituminous  macadam  and  certain  types  of  bituminous 
concrete  pavements,  and  its  use  has  been  extended  to  other 
types  of  pavement.    The  patching  composition  is  composed 
of  unheated  mineral  aggregate  mixed  with  cut-back  asphalt 
(§  98)   or  tar   (§  102)  or  emulsified  asphalt  (§  99).     To  be 
successful    such   bituminous   material    should    possess    the 
property  of  setting  up  rapidly  after  the  mix  is  laid.     The 
physical  and  chemical  properties  of  cold  patching  materials, 
commonly  covered  by  specifications,  are  given  under  Typi- 
cal  Material   Requirements    (§§409,   410).      For  repairing 
bituminous  concrete  pavements  the  mineral  aggregate  should 
preferably  be  of  the  same  approximate  character  and  grad- 
ing as  that  used  in  original  construction.     At  least  one 
sample  of  cold  patching  material  should  be  taken  from 
each  shipment  received. 

334.  Methods,     (a)  Preparation  of  an  old  pavement  to 
receive  patching  mixtures  has  been  covered  under  mainte- 
nance of  the  various  types.     The  patching  composition  is 
usually  mixed  by  hand  on  a  mixing  board  or  platform  but 
sometimes  an  ordinary  concrete  batch  mixer  is  used.     The 
mix  is  proportioned  by  volume,  the  proper  amount  of  bitu- 
minous material  being  dependent  upon  the  character  and 
grading  of  the  mineral  aggregate.     Each  particle  of  aggre- 
gate should  be  thoroughly  and  uniformly  coated   so  as  to 
produce  a  homogeneous  mixture,  but  an  excess  of  bitumin- 
ous material  should  be  avoided  or  otherwise  the  mixture  will 
shove  under  traffic.     If  an  asphalt  emulsion  is  used  the 


Pipe  Culverts  287 

mixing  process  should  be  carried  only,  to  the  point  of  secur- 
ing a  uniformly  coated  aggregate,  as  its  nature  is  such  that 
overmixing  may  cause  the  emulsion  to  separate  and  deposit 
a  film  of  water  on  each  mineral  particle,  thus  destroying  the 
bond  between  asphalt  and  aggregate.  If,  however,  the 
separation  of  the  water  is  allowed  to  occur  gradually  by 
evaporation,  the,  asphalt  will  adhere  firmly  to  a  clean  un- 
coated  aggregate. 

(6)  After  the  mix  has  been  prepared  it  should  be  laid  in 
the  clean  hole  and  tamped  or  rolled  flush  with  the  surround- 
ing area.  The  patch  should  then  be  sanded  or  covered  with 
a  light  dressing  of  stone  chips  after  which  it  should  be 
allowed  to  set  up  for  a  short  while  before  being  subjected  to 
traffic. 

PIPE  CULVERTS 

335.  Clay  and  Concrete  (a)  Vitrified  clay  pipe  are 
usually  specified  to  be  of  the  hub  and  spigot  style,  sound, 
thoroughly  burned,  without  warps,  cracks  or  other  imperfec- 
tions and  to  be  fully  and  smoothly  salt-glazed,  inside  and 
out,  except  that  the  inside  of  the  hub  and  the  outside  of 
spigot  may  be  unglazed  for  two-thirds  of  the  depth  of  the  hub. 
If  the  inside  of  the  hub  and  the  outside  of  the  spigot  are  com- 
pletely glazed  both  should  be  scored  in  a  number  of  parallel 
lines  extending  completely  around  the  circumference.  The 
pipe  should  be  of  such  toughness  that  it  may  be  cut  with  a 
chisel  and  hammer  and  when  struck  should  give  a  metallic 
ring.  When  broken  it  should  show  a  dense  stonelike  struc- 
ture. Typical  specifications  of  the  U.  S.  Bureau  of  Public 
Roads  cover  the  following  minimum  dimensions  for  various 
sizes  of  pipe: 


288       Miscellaneous  Work  and  Materials 


O  " 

Minimum  Dimensions 

. 

bize, 
Inches 

Length,  Feet 

Thickness, 
Inches 

Depth  of  Hub, 
Inches 

12 

2 

1 

3 

15 

2 

H 

3 

18 

2 

H 

3i 

20 

2 

if 

3| 

22 

2 

If 

3.1 

24 

2 

2 

4 

27 

2£ 

2| 

4 

30 

2£ 

2| 

4 

33 

2| 

2| 

5 

36 

2£ 

01 

^4 

5 

42 

2£ 

3| 

5 

(6)  Concrete  pipe  are  usually  specified  to  be  dense,  smooth 
and  free  from  any  imperfection  that  would  impair  their 
strength.  The  concrete  should  be  mixed  in  the  proportion 
of  1  part  standard  Portland  cement  (§  64),  2  parts  sand 
(§  223),  and  1J  parts  clean  pea  gravel,  all  of  which  will  be 
retained  on  a  J-inch  screen.  The  concrete  should  be  thor- 
oughly mixed  with  water  and  tamped  into  proper-shaped* 
forms.  The  use  of  reinforcing  metal  is  ordinarily  specified: 
for  all  sizes  above  12  inches,  and  the  type  of  joint  is  also 
specified.  Typical  specifications  of  the  U.  S.  Bureau  of 
Public  Roads  cover  the  following  requirements  in  connec- 
tion with  thickness  and  the  weight  of  triangular  mesh,  or 
other  approved,  reinforcement  for  various  sizes  of  pipe. 


Inside 

Minimum  Thickness, 

Triangular  Reinforcement, 

Diameter 

Inches 

4"-mesh.  Minimum  Weight 

12 

2 

No  Reinforcement 

18 

2 

0.30  Lbs.  per  sq.  ft. 

24 

2| 

0.40 

(     a 

* 

30 

3 

0.40 

(     a 

f  -• 

36 

31 

0.50 

(     a 

14  1 

42 

0.60 

48 

4 

0.60 

i     it 

Pipe  Culverts  289 

(c)  Standard  specifications  for  drain  tile  manufactured 
from  shale,  fire  clay,  surface  clay  and  concrete  have  been 
adopted  by  the  American  Society  for  Testing  Materials 
under  serial  designation  C4-16.  These  specifications  cover 
;  limitations  for  tests  of  strength,  absorption,  and  freezing 
and  thawing  for  three  classes  of  tile  known  as  farm  drain 
tile,  standard  drain  tile  and  extra  quality  drain  tile,  the  class 
to  be  specified  by  the  purchaser.  These  specifications  re- 
quire that  a  sample  for  physical  test  shall  consist  of  five 
individual  tile.  Visual  inspection  is  covered  in  consider- 
able detail.  Among  the  points  covered,  the  following  are 
probably  the  most  important  from  the  standpoint  of  high- 
way inspection.  Unless  otherwise  specified,  all  drain  tile 
should  be  of  approximately  circular  cross  section  and  ap- 
proximately straight,  with  ends  sufficiently  regular  and 
smooth  to  admit  of  making  close  joints  by  turning  and  press- 
ing together  adjoining  tile.  Sizes  should  be  designated  by 
the  internal  diameter.  Tile  smaller  than  12  inches  in  diame- 
ter should  have  a  minimum  length  of  12  inches.  From 
12-  to  30-inch  tile  should  have  a  length  not  less  than  their 
diameter  and  if  larger  than  30-inch  the  length  should  be  not 
less  than  30  inches.  They  should  be  uniform  in  structure 
throughout,  reasonably  smooth  on  the  inside  and  free  from 
cracks  or  checks  which  would  appreciably  affect  their 
strength.  They  should  not  be  chipped  or  broken  in  such 
manner  as  to  decrease  their  strength  materially,  or  admit 
earth  into  the  drain.  They  should  be  vitrified  or  hard 
burned  and  when  stood  on  end  in  a  dry  condition  and 
tapped  with  a  light  hammer  they  should  give  a  clear  ring. 
For  extra  quality  tile  a  tolerance  of  3  per  cent  in  average 
diameter  below  that  specified  is  allowed.  Sixty-five  per 
cent  of  the  thickness  of  wall  is  given  as  an  allowable  varia- 
tion between  maximum  and  minimum  diameters  of  the 
same  tile  or  average  diameters  of  adjoining  tile.  The  toler- 
ance for  straightness  is  an  allowance  of  3  per  cent  of  the 
length.  The  allowable  thickness  of  exterior  blisters,  lumps 


290        Miscellaneous  Work  and  Materials 

and  flakes  which  do  not  weaken  the  tile  and  are  few  in 
number  is  given  as  15  per  cent  of  the  thickness  of  wall.  The 
allowable  diameters  of  such  blisters,  lumps  and  flakes  is  10 
per  cent  of  the  internal  diameter. 

336.  Metal  Pipes,  (a)  Corrugated  metal  pipes  are  con- 
structed of  both  iron  and  steel  and  the  chemical  composi- 
tion of  the  base  metal  is  sometimes  specified  in  great  detail. 
The  minimum  weight  per  t  square  foot  of  spelter  coating,  or 
galvanizing,  is  also  specified  as  determined  by  laboratory 
test.  Typical  specifications  of  the  U.  S.  Bureau  of  Public 
Roads  allow  either  iron  or  steel  as  the  base  metal  without 
any  definite  chemical  requirements  and  require  not  less 
than  2  ounces  of  prime  spelter  per  square  foot  of  sheet, 
uniformly  distributed  over  the  surfaces  of  the  sheets  of 
metal.  They  further  require  that  the  sheets  of  metal  be- 
fore galvanizing  shall  be  smooth  and  free  from  blisters, 
seams  and  pits,  and  shall  be  not  less  than  16-gauge  U.  S. 
Standard  for  pipe  of  20-inch  diameter  or  less,  and  not  less 
than  14-gauge  U.  S.  Standard  for  pipe  between  20  and  36 
inches  in  diameter.  They  also  require  that  the  spelter  shall 
be  applied  in  such  manner  that  it  will  not  peel  off  during 
fabrication,  transportation  or  laying  of  the  pipe,  and  that 
any  uncoated  spots  due  to  poor  workmanship,  rough  han- 
dling or  any  other  reason  shall  be  sufficient  cause  for  rejec- 
tion. Other  points  which  may  be  determined  by  visual 
inspection  are  as  follows:  "The  corrugations  shall  be  not 
less  than  2|  inches  nor  more  than  3  inches  from  crest  to 
crest  and  shall  have  a  depth  of  not  less  than  \  inch  nor  more 
than  |  inch.  All  joints  shall  be  even  and  close  and  the 
jointed  pipe  shall  be  straight,  circular  in  section,  true  and 
rigid.  In  the  longitudinal  joints,  rivets  shall  be  driven  in 
the  valley  of  each  corrugation;  in  the  transverse  joints 
rivets  shall  be  uniformly  spaced  not  more  than  6  inches 
apart.  The  rivets  shall  be  at  least  one  inch  from  the  edge 
of  the  sheet  and  shall  be  driven  in  such  manner  as  to  draw 
the  sheets  tightly  together  and  fill  the  rivet  holes  com- 


Pipe  Culverts 


291 


pletely.  All  rivets  shall  be  thoroughly  galvanized  and  shall 
be  not  less  than  f^  inch  in  diameter,  with  neat  semi-spherical 
or  flat  heads.  The  heads  shall  have  a  diameter  of  not  less 
than  one  and  one-eighth  times  the  diameter  of  the  rivet,  plus 
|  inch,  and  all  flat  heads  shall  have  a  thickness  not  less  than 
four-tenths  that  of  the  diameter  of  the  rivet.  Field  connec- 
tions shall  consist  of  bands  not  less  than  8  inches  in  width  so 
fabricated  that  a  secure  and  firm  connection  of  the  sections 
of  pipe  may  readily  be  made.  The  diameter  of  the  pipe 
shall  be  understood  to  mean  the  clear  diameter."  Unless 
the  pipe  has  been  inspected  at  the  plant  the  Inspector  should 
take  a  sample  from  each  size  pipe  in  each  consignment,  but 
in  no  case  should  less  than  3  samples  be  taken  from  each 
consignment.  Each  sample  should  be  cut  out  with  a  cold 
chisel  and  should  measure  about  6  inches  square. 

(6)  Cast-iron  pipe  are  usually  made  with  bell  and  spigot 
joints.  They  should  be  straight  and  the  inner  and  outer 
surfaces  should  be  true  concentric  cylinders.  All  samples 
should  be  smooth,  free  from  scales,  lumps,  blisters,  sand 
holes  and  defects  of  every  nature  which  would  unfit  the 
pipe  for  the  use  for  which  it  is  intended.  Each  pipe  should 
be  coated  inside  and  out  with  a  bituminous  paint.  Typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads  give  the 
following  minimum  thickness  and  weight  per  foot  of  cast- 
iron  pipes  of  various  sizes,  and  allow  a  tolerance  of  5  per 
cent  on  minimum  weight. 


Inside  Diameter 

Minimum  Thickness, 
Inches 

Minimum  Weight  per 
cu.  ft.,  Pounds 

12 
14 
16 
18 
20 
.    24 
30 
36 

0.54 
.57 
.60 
.64 
.67 
.76 
.88 
.99 

72.5 

89.6 
108.3 
129.2 
150.0 
204.2 
291.7 
391.7 

292       Miscellaneous  Work  and  Materials 

337.  Joints.  For  cementing  pipe  joints,  cement  mortar, 
consisting  of  1  part  of  standard  Portland  cement  and  2  parts 
of  concrete  sand  (§  223),  or  a  bituminous  joint  filler  is  used. 


CONCRETE  FOR  MISCELLANEOUS  STRUCTURES 

338.  Classes   of   Concrete.     Concrete   for   structures   is 
usually  divided  into  two  or  more  classes  which  are  designated 
by  letter  as  Class  A,  Class  B,  etc.    Different  proportions  of 
standard  Portland  cement,  fine  aggregate  and  coarse  aggre- 
gate, and  frequently  different  size  or  grading  limitations  for 
fine  and  coarse  aggregate  are  specified  for  each  class.    Both 
proportions  and  grading  limitations  are  selected  with  refer- 
ence to  the  character  and  importance  of  the  structure  in 
which   the    concrete   is    to    be    used.    The   maximum  size 
fragment  of  coarse  aggregate  may  also  be  determined  in 
reinforced  structures  by  the  minimum  space  between  rein- 
forcing bars  or  the  minimum  space  between  surface  and  rein- 
forcing metal.     The  proportioning  and  mixing  of  concrete 
for  structures,  as  well  as  the  inspection  of  work  and  sam- 
pling of  materials,  is  in  general  similar  to  that  described 
for  concrete  foundations  and  pavements  (Chapter  XI). 

339.  Field  Test  for  Cement     In   case  a  very  limited 
amount  of  concrete  is  to  be  used  in  structures  of  minor  im- 
portance, such  as  head  walls  for  pipe  culverts,  and  the  cement 
has  not  been  previously  tested,  the  Inspector  may  make  the 
following  test.     A  small  amount  of  the  cement  should  be 
kneaded  with  enough  water  to  form  a  stiff  paste,  which  is 
formed  into  a  ball  about  1J  inches  in  diameter.     The  ball 
should  then  be  placed  under  a  damp  cloth  and  at  intervals 
tested  with  the  point  of  a  lead  pencil  to  see  that  it  does  not 
set  too  rapidly  (§  80).    The  ball  should  be  allowed  to  remain 
under  the  damp  cloth  over  night  and  should  then  be  placed 
for  three  hours  in  a  pan  of  boiling  water.    If  it  is  then,  hard 
and  free  from  check  marks  the  cement  is  sound.    While  this 
test  may  serve  as  an  emergency  method  for  small  structures, 


Concrete  for  Miscellaneous  Structures       293 

it  should  never  be  relied  upon  for  important  concrete  struc- 
tures where  the  higher  classes  of  concrete  are  used. 

340.  Forms.  Structural  concrete  is  usually  placed  and 
tamped  in  specially  constructed  forms  which  are  often  sup- 
ported by  falsework.  All  forms  should  be  designed  and 
constructed  so  that  they  may  be  removed  without  injuring 
the  concrete.  As  an  example  of  specification  requirements 
for  form  work  the  following  is  taken  from  typical  specifica- 
tions of  the  U.  S.  Bureau  of  Public  Roads:  "The  material 
to  be  used  in  the  forms  for  exposed  surfaces  shall  be  sized 
and  dressed  lumber,  or  metal  in  which  all  bolt  and  rivet 
heads  are  countersunk,  so  that  in  either  case  a  plain  smooth 
surface  of  the  desired  contour  is  obtained.  Undressed  lum- 
ber may  be  used  for  backing  or  other  unexposed  surfaces. 
The  forms  shall  be  built  true  to  line  and  braced  in  a  sub- 
stantial and  unyielding  manner.  They  shall  be  mortar- 
tight  and,  if  necessary  to  close  cracks  due  to  shrinkage,  shall  be 
thoroughly  soaked  with  water.  Forms  for  reentrant  angles 
shall  be  chamfered  and  for  corners  shall  be  filleted.  Dimen- 
sions affecting  the  construction  of  subsequent  portions  of 
the  work  shall  be  carefully  checked  after  the  forms  are 
erected  and  before  any  concrete  is  placed.  The  interior 
surfaces  of  the  forms  shall  be  adequately  oiled,  greased  or 
soaped  to  insure  the  non-adhesion  of  mortar.  Form  lumber 
which  is  to  be  used  a  second  time  shall  be  free  from  bulge  or 
warp  and  shall  be  thoroughly  cleaned.  The  forms  shall  be 
inspected  immediately  preceding  the  placing  of  concrete, 
and  any  bulging  or  warping  shall  be  remedied  and  all  dirt, 
sawdust,  shavings  or  other  debris  within  the  forms  shall 
be  removed."  The  placing  of  concrete  within  forms  should 
be  as  continuous  as  possible,  and  wherever  new  concrete 
is  placed  against  concrete  which  has  reached  its  initial  set, 
such  juncture  should  be  considered  and  planned  for  as  a 
construction  joint.  Regular  expansion  joints  are  provided 
for  in  certain  concrete  structures,  as  in  the  case  of  pavements 
(§§328-330).  The  tune  and  condition  under  which  forms 


294       Miscellaneous  Work  and  Materials 

may  be  removed,  depending  upon  the  type  of  structure, 
should  be  covered  by  the  specifications  and  closely  observed 
by  the  Inspector.  After  removal  of  the  forms  the  exposed 
surface  may  be  smoothed  up  by  filling  small  cavities  with 
cement  mortar  and  rubbing  the  surface  free  of  form  marks 
with  a  wooden  float  and  clean  water.  Various  kinds  of  sur- 
face finish  may  also  be  specified. 

341.  Waterproofing.     Structural    concrete    is    sometimes 
waterproofed  by  incorporating  hydrated  lime  in  the  mix  to 
the  extent  of  about  10  per  cent  of  the  volume  of  cement 
used.    The  lime  is  ordinarily  required  to  meet  the  specifica- 
tions of  the  American  Society  for  Testing  Materials  adopted 
as  Standard  C6-15  (§226). 

IRON  AND   STEEL 

342.  Reinforcing,     (a)  Metal  reinforcement  for  concrete 
structures  usually  consists  of  square  twisted,  deformed  or 
plain  steel  bars,  expanded  metal,  wire  mesh  or  wire  cloth, 
or  structural  steel  shapes,  as  specified  or  called  for  on  the 
plans.    The  Inspector  should  see  that  it  is  placed  in  accord- 
ance with  plans  and  specifications. 

(6)  Steel  bars  may  be  made  from  billet  steel  or  from  re- 
rolled  rail.  Specifications  for  the  former  have  been  adopted 
as  Standard  A15-14  and  for  the  latter  as  Standard  A16-14 
by  the  American  Society  for  Testing  Materials.  These 
specifications  cover  various  chemical  and  physical  proper- 
ties, which  can  only  be  determined  by  laboratory  test  and 
inspection,  and  sampling  for  work  of  any  magnitude  should 
be  conducted  at  the  point  of  manufacture.  The  Highway 
Inspector  should,  however,  subject  the  reinforcement  to 
visual  inspection  and,  if  laboratory  test  records  are  not 
available,  he  may  sometimes  subject  specimens  to  the  cold 
bend  test  by  means  of  the  equipment  operated  by  the  con- 
tractor for  bending  bars.  From  billet  steel  three  grades  are 
manufactured,  which  are  known  as  structural  steel,  inter- 


Iron  and  Steel 


295 


mediate  and  hard.  The  desired  grade  should  be  indicated 
in  the  specification.  The  cold  bend  test  is  made  by  bending 
the  test  specimen  around  a  pin  for  180  degrees  or  90  degrees 
as  called  for,  under  which  test  the  specimen  should  show  no 
cracking  on  the  outside  of  the  bent  portion.  In  the  follow- 
ing table  are  shown  the  diameters  of  pins  and  the  degrees 
of  bending  required  of  the  various  types  and  grades  of  bars, 
with  diameters  under  f  inch  and  diameters  of  f  inch  or  over. 
In  this  table  t  represents  the  diameter  of  the  specimen  which 
is  bent. 

COLD-BEND  TEST  REQUIREMENTS 


Type  and  Grade  of  Bar 

Thickness  or  Diameter  of  Bar 

Less  than  f  Inch 

f  Inch  or  Over 

Deg. 

Diam. 

Deg. 

Diam. 

Bend 

Pin 

Bend 

Pin 

I. 

Plain  Bars: 

Billet,  Structural      

180 

t 

180 

t 

Billet,  Intermediate  

180 

21 

90 

2t 

Billet,  Hard 

180 

3t 

90 

3t 

Rail. 

180 

3t 

90 

3t 

TI. 

Deformed  Bars: 

Billet,  Structural 

180 

t 

180 

2t 

Billet,  Intermediate  

180 

3< 

90 

3t 

Billet,  Hard  180 

At 

90 

U 

Rail  

180 

M 

90 

U 

ITT. 

Cold  Twisted  Bars: 

Billet                         .    ... 

180 

2t 

180 

31 

IV. 

Hot  Twisted  Bars: 

Rail 

Twisted  bars  are  required  to  have  one  complete  twist  in 
a  length  not  over  12  times  the  thickness  of  the  bar.  All 
bars  are  specified  to  be  free  from  injurious  defects  and  to 
have  a  workmanlike  finish.  The  weight  of  any  lot  of  bars 
should  not  vary  more  than  5  per  cent  from  the  theoretical 
weight  of  that  lot. 


296       Miscellaneous  Work  and  Materials 

(c)  Expanded  metal  and  wire  mesh  or  wire  cloth  rein- 
forcement, in  addition  to  limitations  of  physical  properties 
determined  by  laboratory  test,  are  usually  specified  to  have 
a  certain  minimum  weight  per  100  square  feet.  Such  weight 
may  be  determined  by  the  Inspector. 

343.  Structural    Steel.     Structural    steel    and    iron    are 
manufactured  and  fabricated  in  accordance  with  plans  and 
specifications.    Plain  structural  shapes,  fabricated  structural 
steel  and  steel  rivets,  as  well  as  steel  and  iron  castings,  are 
usually   required   to   meet    certain   standard   specifications 
ad'opted  by  the  American  Society  for  Testing  Materials. 
Inspection  of  structural  steel  for  important  work  should 
be  conducted  at  the  plant. 

MASONRY 

344.  Types  of  Masonry,     (a)  There  are  two  types   of 
masonry  commonly  used  in  connection  with  highway  struc- 
tures, brick  masonry  and  rubble  masonry.    Brick  are  usually 
laid  in  cement  mortar.     Rubble,  laid  in  cement  mortar,  is 
known  as  cement  rubble  masonry,  and  laid  without  mortar, 
as  dry  rubble  masonry. 

(6)  Brick  are  usually  specified  as  to  quality,  size  and  some- 
times color  and  are  required  to  have  straight  parallel  edges 
and  square  corners.  They  should  be  hard  burned  through- 
out, of  uniform  texture  and  free  from  cracks  or  injurious 
defects.  They  are  sometimes  culled  with  a  view  to  using 
the  most  uniform  brick  in  the  face  of  the  masonry.  The 
only  test  to  which  they  are  ordinarily  subjected  is  one  for 
absorption,  and  specifications  often  require  that  when 
thoroughly  dried  and  weighed  they  shall  not  absorb  more 
than  10  per  cent  of  water  upon  24  hours'  immerson.  They 
may  also  be  required  to  give  forth  a  clear  ringing  sound 
when  struck  sharply  together. 

(c)  Rubble  stones  should  be  sound  and  free  from  structural 
defects,  earth,  clay  or  other  foreign  substances.  Selected 


Preservative  Coatings  297 

stones  roughly  squared  and  pitched  to  line  are  usually  used 
at  angles  and  ends  of  structures.  The  approximate  dimen- 
sions of  stones  in  the  face  of  the  masonry  are  generally 
specified  but  smaller  stones  are  allowed  for  filling  joints. 

345.  Mortar.  Mortar  for  laying  brick  and  rubble 
masonry  is  ordinarily  composed  of  one  part  of  standard 
Portland  cement  to  3  parts  of  sand,  while  for  pointing  a 
1  :  1  mortar  is  used.  Hydrated  lime  is  ordinarily  added  to 
the  extent  of  ten  per  cent  by  volume  of  cement.  A  full 
mortar  bed  is  used  for  the  brick  or  rubble  stone  which 
should  be  thoroughly  soaked  before  laying.  Brick  are  laid 
in  the  mortar  so  as  to  break  joints  about  J  brick  between 
courses.  On  exposed  faces  of  all  masonry  the  joints  should 
be  cleaned  or  raked  out  and  pointed  with  the  1  : 1  mortar. 


PRESERVATIVE  COATINGS 

346.  Paints.     Wood    and   steel   highway   structures   are 
usually  coated  with  paint  which  should  be  carefully  speci- 
fied as  to  composition.    The  paint  is  ordinarily  composed  of 
a  pigment,  such  as  a  metallic  oxide,  sulphate,  or  carbonate, 
ground  in  linseed  oil  and  thinned  with  turpentine  which 
serves  as  a  drier.     They  are  sometimes    purchased   ready 
for  use  and  sometimes  a  paint  paste  is  purchased  and  mixed 
with  thinner,  to  proper  consistency,  on  the  job.     The  In- 
spector should  take  and  submit  to  the  laboratory  a  one-pint 
sample  of   prepared  paint  or  of   each  individual   constitu- 
ent used  on  the  job  from  each  shipment  received. 

347.  Dips.     Specifications  frequently  require  that  posts 
which  are  to  be  partially  buried  in  the  ground,  such  as  posts 
for  guard  rails,  should  be  painted  with  or  dipped  in  a  bitu- 
minous paint  for  the  depth  to  which  they  are  to  be  buried. 
A  coal   tar  paint  is  frequently  specified  for  this   purpose. 
A    one-quart   sample    of    such    paints   or   dips   should   be 
taken  from  each  shipment  received  and  submitted  to  the 
laboratory  for  examination. 


298       Miscellaneous  Work  and  Materials 

NON-BITUMINOUS  DUST  PREVENTIVES  AND 
BINDERS 

348.  Calcium  Chloride.     Calcium  chloride  is  a  chemical 
substance    obtained   in   large   quantities    as    a   by-product 
mainly  in  the  manufacture  of  soda  from  salt.     It  may  be 
obtained  as  a  solid  or  in  concentrated  solution,  but  the  granu- 
lated solid  is  the  most  common  form  in  which  it  is  now  used 
for    highway    purposes.      Calcium    chloride    has    a    strong 
affinity  for  water  and  will  absorb  moisture  from  the  atmos- 
phere to  such  an  extent  that  in  humid  weather  it  will  dis- 
solve in  the  water  thus  absorbed.     It  has  been  used  to  a 
considerable  extent  as   a  dust  preventive  for  broken  stone 
or  gravel  roads  and  to  a  limited  extent  in  the  construction 
of  such  roads.    For  surface  treatment  when  used  in  granu- 
lated form  it  may  be  spread  by  means  of  shovels  at  the 
specified  rate  of  application,  usually  from  1  to  2  pounds  per 
square  yard,  but  the  use  of  a  fertilizer  distributor  is  more 
satisfactory.    In  solution  it  is  applied  by  means  of  an  ordi- 
nary street  sprinkler.     Its  effect  as  a  dust  preventive  is 
much  more  lasting  than  water  but  reapplications  are  neces- 
sary at  intervals,  depending  upon  climatic  and  other  local 
conditions.    A  one-pound  sample  of  the  solid  or  a  one-quart 
sample  of  the   liquid  should  be  taken  from  each  shipment 
received  and  submitted  to  the  laboratory. 

349.  Sodium    Silicate.     Sodium    silicate    is    a    chemical 
substance  commonly  sold  in  the  form  of  a  thick  syrupy 
liquid  known  as  water  glass.     Upon  exposure  to  the  atmos- 
phere it  precipitates  gelatinous  silicic  acid,  and  reacts  with 
calcareous  rocks  to  form  calcium  silicate  upon  the  surface 
of  the  rock  fragments.     It  is.  extensively  used  as  a  binder 
in  the  manufacture  of  artificial  rock  and  is  used  as  the  basis 
of  a  patented  road  material  known  as  "Rocmac."     The 
Rocmac  solution  may  be  mixed  with  limestone  screenings, 
at  the  rate  of  15  gallons  per  cubic  yard,  to  form  a  matrix 
which  is  spread  upon  the  road  to  a  thickness  of  J  inch 


Dust  Preventives  and  Binders  299 

for  every  1  inch  thickness  of  broken  stone  which  it  is  re- 
quired to  bind.  Broken  stone  is  then  spread  and  rolled 
until  the  matrix  works  to  the  top.  If  desired  a  mixture  of 
the  solution  with  limestone  screenings  and  broken  stone 
may  be  prepared  in  a  concrete  mixer  and  the  resulting 
product  laid  and  compacted  as  in  ordinary  macadam  con- 
struction. 

350.  Waste  Sulphite  Liquor.  In  the  manufacture  of 
wood  pulp,  according  to  the  sulphite  process  a  waste  liquor 
is  produced  in  large  quantities.  By  partial  evaporation  a 
thick  syrupy  residue  is  produced  which  possesses  consider- 
able binding  value.  Such  a  concentrated  product,  known 
as  "Glutrin, "  is  marketed  as  a  road  material  and  has  been 
used  to  some  extent  as  a  dust  layer  and  binder  for  macadam 
and  gravel  roads.  It  may  be  diluted  with  water  to  any 
desired  extent  and  applied  by  means  of  an  ordinary  street 
sprinkler.  The  proportions  of  Glutrin  and  water  most 
commonly  used  lie  between  1  :  10  and  1  : 20.  The  number 
of  treatments  required  for  a  season  depends  upon  traffic 
and  climatic  conditions. 


CHAPTER  XVI 

MEASUREMENTS 
GENERAL  CONSIDERATIONS 

351.  Purpose  of  Measurements.    Measurements  should 
be  taken  and  recorded  by  the  Inspector  for  the  purpose  of 
ascertaining  quantities  of  materials  received  and  used,  or 
amount  of  work  performed,  in  accordance  with  specification 
requirements.    In  certain  instances  measurements  may  also 
serve  to  determine  the  character  of  work  performed. 

352.  Classes  of  Measurement.     There  are  four  principal 
classes  of  measurement  considered  in  the  following  para- 
graphs.    These  are  linear  measurement,  measurements  of 
area,  measurements  of  volume  and  measurements  of  weight. 
Other  classes,  such  as  measurements  of  temperature  and 
time,  require  no  special  comment. 

353.  Accuracy  of  Measurements.    Measurements  made 
by  the  Inspector  can  be  accurate  only  to  the  extent  that 
they  are  truly  representative.     This  may  necessitate  fre- 
quent check  measurements  and  recourse  to  different  methods. 
Thus,  the  average  depth  of  a  pavement  can  only  be  ascer- 
tained by  a  number  of  measurements  of  depth  judiciously 
made,  and  accuracy  of  volume  measurements  may  require 
checking  by  measurements  of  weight.    In  some  instances  it 
may  also  be  necessary  to  take  into  account  certain  factors, 
such  as  expansion,  contraction  or  shrinkage,  and  wastage, 
which  will  vary  considerably  at  times  even  for  the  same 
type  of  work  or  same  class  of  material.     The  Inspector's 
basis  of  measurement  may  also  differ  from  that  of    the 
Engineer  as  later  explained.     All  of  these  facts  should  be 

300 


Linear  Measurements  301 

clearly  understood  and  borne  in  mind  in  order  to  prevent 
confusion  and  unnecessary  controversy. 


LINEAR  MEASUREMENTS 

354.  Length,  (a)  The  common  unit  of  measure,  for 
length  of  highway,  is  the  foot  and  the  basis  of  measure  the 
center  line  of  the  highway  surface.  On  the  plans,  a  hori- 
zontal base  line  is  shown  or  indicated  which,  commencing 
at  a  given  zero  point,  is  divided  into  sections  of  100  feet 
each.  The  point  of  juncture  of  two  sections  is  called,  a 
station  and  is  given  a  number  known  as  a  station  number. 
Thus,  station  1  indicates  100  feet  measured  horizontally 
from  the  zero  point  on  the  base  line;  station  2  indicates 
200  feet,  etc.  Intermediate  points  in  a  station  are  expressed 
in  feet  and  decimal  parts  of  a  foot.  Thus,  Station  12+50.1 
means  1250.1  feet  measured  horizontally  from  the  zero 
point  on  the  base  line.  Stations  at  the  center  line  of  the 
highway  are  fixed  by  vertical  projections  of  the  base-line 
stations.  It  is  evident  that  if  the  surface  of  the  highway 
is  parallel  to  the  base  line  or,  in  other  words,  is  level,  station 
distances  on  the  center  line  are  the  same  as  on  the  base  line 
and  each  center-line  section  is,  therefore,  100  feet  in  length. 
If,  on  the  other  hand,  the  center  line  runs  at  an  angle  to 
the  base  line,  or,  in  ordinary  terms,  runs  up  or  down  grade, 
station  distances  on  the  center  line  will  be  greater  than  on 
the  base  line.  The  actual  distance,  may  be  calculated,  if 
the  difference  in  elevation  between  two  points  on  the  center 
line  is  known  and  between  these  points  the  angle,  of  the 
center  line  to  the  base  line,  is  a  constant.  Under  such 
conditions  the  difference  in  elevation  is  called  the  grade 
of  the  road  and  is  expressed  in  per  cent  of  the  corresponding 
section  of  base  line.  Thus,  a  5-per-cent  grade  means  a  uni- 
form rise  or  fall  of  center  line  of  5  feet  per  100  feet  of  base 
line.  Up  to  5-per-cent  grades  the  difference  in  center-line 
and  base-line  distances  is  within  the  allowable  limit  of  error 


302  Measurements 

of  ordinary  measurement  and  need  not  be  considered. 
Above  5-per-cent  grades  it  becomes  noticeable.  The  dif- 
ferences between  stations,  distances  and  center-line  dis- 
tances for  various  grades  is  shown  in  the  following  table: 


Per  cent  Feet,  Center  Line 

Grade  per  Station 


5 100.13 

6 100.18 

7 100.25 

8 UU.3i>  100.32 

9 100.40 

10 ..  .  100.50 

11 ....  100.60 

12..  100.72 


(6)  On  tangents  or  straight  sections  of  highways,  sta- 
tions at  the  side  of  the  highway  are  the  same  distance  apart 
as  at  the  center  line.  On  curves,  however,  the  distances 
vary  according  to  the  radius  of  the  curve  at  the  side  station 
or  the  distance  of  the  side  station  from  the  center  of  the 
circle  bounded  by  a  completion  of  the  curve.  For  this 
reason,  all  measurements  of  length  should  be  made  along 
the  center  line. 

355.  Width.    The  width  of  a  highway  is  measured  at 
right  angles  to  the  center  line  on  tangents,  and  on  the  radius 
of  curves.     The  width  of  pavement  proper  is  the  shortest 
distance  between  the  inside  edges  of  shoulders,  gutters,  or 
curbs,  as  the  case  may  be,  but  the  effect  of  crown  is  so  slight 
that  no  important  error  is  made  by  measuring  directly  across 
the  surface  for  crowns  of  J  inch  or  less.    For  crowns  greater 
than  \  inch  a  plumb  line  should  be  used  in  connection  with 
the  tape. 

356.  Thickness,     (a)  Thickness   or   depth   of   pavement 
is,  in  most  cases,  much  more  difficult  to  control,  and  meas- 
ure with  accuracy,  than  width  or  length.     Uniform  depth 
of  a  pavement  true  to  grade  and  line  can  only  be  secured  by 


Linear  Measurements  303 

similar  conditions  in  the  subgrade  or  underlying  course. 
Differences  in  thickness  at  different  locations  in  the  cross 
section,  such  as  center  and  sides,  are  often  specified  and 
must  necessarily  exist  unless  the  underlying  surface  carries 
the  same  crown  as  the  pavement  proper.  In  either  case, 
frequent  measurements  of  depth  at  representative  points 
should  be  made  by  the  Inspector. 

(6)  Uncompacted  thickness  is  often  gauged,  in  the  case 
of  materials  which  are  spread,  by  the  use  of  wooden  cubes 
of  suitable  dimensions  which  are  laid  at  intervals  across  the 
highway  on  the  subgrade  or  underlying  course.  These 
cubes  are  moved  along  as  the  work  progresses.  This  method 
is  satisfactory  if  the  subgrade  or  underlying  course  is  free 
from  irregularities,  but,  if  irregularities  exist,  they  are  apt 
to  be  carried  up  to  the  surface  of  the  pavement.  It  is  ordi- 
narily considered  better  practice  to  set  gauge  strings  longi- 
tudinally at  the  sides  and  center  of  the  highway. 

(c)  For  some  classes  of  work  a  template  is  used  not  only 
for  securing  the  desired  contour  but  also  the  desired  thick- 
ness. In  the  latter  case  the  template  is  worked  at  right 
angles  to  the  center  line  of  the  highway  from  side  forms, 
curbs,  or  edging  set  at  the  proper  elevation.  Distance  from 
points  on  the  under  face  of  the  template  to  the  subgrade  or 
underlying  surface  should  be  measured  from  time  to  time 
as  a  check. 

357.  Testing  Contours  and  Surface  Irregularities.  Speci- 
fications frequently  require  that  finished  surfaces  shall  be 
tested  with  a  straightedge,  or  with  a  template  cut  to  the 
crown  shown  on  the  cross-section  drawings.  In  the  case  of 
a  straightedge,  its  length  and  method  of  use  are  specified. 
If  a  template  is  used,  the  surface  is  tested  at  right  angles  to 
the  center  line.  If  template  and  straightedge  are  both 
specified,  the  straightedge  is  used  for  testing  the  surface 
longitudinally,  in  which  case  it  may  be  eight  feet  or  more 
in  length.  If  a  straight  edge  only  is  specified,  it  is  usually 
made  about  2  feet  in  length  and  the  tests  are  made  by  lay- 


304 


Measurements 


ing  it,  in  various  directions,  on  the  surface.  Maximum 
allowable  depth  of  depressions,  under  such  test,  is  speci- 
fied, and  all  depressions  approximating  the  specified  limit 
should  be  measured  by  the  Inspector. 

MEASUREMENTS  OF  AREA 

358.   Surface  Areas,     (a)  The  common  unit  of  measure 
for  surface  area  of  highway  is  the  square  yard.    In  estimat- 


^^•* 

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100                 120                 140 

160                  180                 2(M 

SQUARE  YARDS  PER  100  LINEAR  FEET 
Fig.  39     Area  of  100  Linear  Feet  of  Road 


Measurements  of  Area  305 

ing  and  checking  quantities  of  materials  used,  the  Inspector 
is  interested  only  in  actual  surface  yardage.  Payment  is, 
however,  frequently  made  upon  horizontal  measurement  so 
that  there  may  be  the  same  relative  discrepancy  between 
actual  and  horizontal  area  measurements  as  shown  under 
measurements  of  length  (§354).  Thus,  the  horizontal 
yardage  of  900  feet  of  highway  18  feet  wide  on  a  7-per-cent 
grade  is 

900  x  18      1cnn 
— =  1800  sq.  yds. 

while  the  actual  yardage  is 

9  x  100.25  X  18 


9 


=  1804.5  sq.  yds. 


(b)  The  number  of  square  yards  of  surface  per  100  feet 
of  highway  of  various  widths  is  shown  in  Fig.  39.  The 
number  of  square  yards  per  foot  of  highway  may  also  be 
obtained  from  this  diagram  by  pointing  off  two  decimals 
for  the  values  given.  The  equivalent  of  100  square  yards 
of  surface,  in  linear  feet  of  highway,  and  the  equivalent  of 
1  square  yard,  in  linear  inches  of  highway  are  shown  in  Figs. 
40  and  41  for  different  widths  of  road. 

359.  Crown  Sections,  (a)  In  estimating  the  volume  of 
material  in  a  given  length  and  width  of  highway,  it  is  neces- 
sary to  know  the  depth.  Unless  the  depth  is  the  same 
throughout  the  width,  this  involves  a  determination  of 
average  depth  or  else  a  determination  of  the  area  of  the 
cross  section  of  the  highway.  The  la'ter  method  is  most 
convenient  when  the  crown  is  curved  and  may  best  be  used 
by  considering  crown  section  areas,  first  of  all,  as  distinct 
from  total  end  section  areas.  The  crown  of  a  road  or  pave- 
ment is  usually  expressed  as  average  difference  of  eleva- 
tion in  fractions  of  an  inch  per  foot  of  width.  Thus  a  crown 
of  J  inch  means  an  average  drop,  from  peak  of  crown  to 
edge  of  road,  of  i  inch  per  foot.  Except  on  sharp  curves 
where  the  surface  is  sometimes  made  to  slope  in  a  single 


306 


Measurements 


direction,  the  peak  of  the  crown  is  carried  along  the  center 
line  of  the  highway. 

(b)  While  various  crown  formulas  have   been  used,  the 
three  most  common  types  of  crown  are  the  intersection  of 


12  16  20  24  28  32  36 

WIDTH  OF  ROAD,  FEET 

Fig.  40     Length  of  Road  Represented  by  100  Square  Yards 


two  straight  lines,  the  parabola  and  the  circular  arc.  The 
crown  section  is  the  area  enclosed  by  connecting  the  lower 
extremities  of  the  crown  with  a  straight  line.  In  the  case 
of  the  crown,  made  by  the  intersection  of  two  straight  lines, 
this  will  produce  a  triangle,  the  area  of  which  is  equal  to 


Measurements  of  Area 


307 


the  width  of  the  road  multiplied  by  one-half  the  difference 
in  elevation  between  the  center  and  sides.  In  the  case  of  a 
parabolic  crown,  the  area  of  the  crown  section  is  equal  to  the 
width  of  the  road  multiplied  by  two-thirds  the  difference  in 


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WIDTH  OF  ROAD,  FEET 


32 


Fig.  41     Length  of  Road  Represented  by  One  Square  Yard 

elevation  between  the  center  and  sides.  No  such  definite 
relation  exists  for  the  circular  arc  crown  but  ordinarily  it  is 
so  close  to  the  parabolic  that  for  all  practical  purposes  the 
same  formula  may  be  used.  Upon  this  basis  Fig.  42  shows 
the  crown  section  areas  for  pavements  of  different  width, 


308 


36 


32 


Measurements 

WIDTH  OF  ROAD,  FEET 


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9          12  16  20  24  28  32  36 

WIDTH  OF  ROAD,  FEET 

Fig.  42     Crown  Section  Areas 

for  various  differences  in  elevation  between  the  center  and 
sides.    This  difference  is  called  the  total  crown. 


Measurements  of  Area  309 

360.  End  Section  Areas,  (a)  The  end  section  of  a  pave- 
ment represents  an  area  bounded  at  the  top  by  the  crown 
of  the  pavement,  at  the  bottom  by  the  line  of  juncture  with 
the  underlying  course  or  subgrade,  and  at  the  sides  by  the 
inside  faces  of  shoulders,  gutters  or  curbs.  The  underlying 
course  or  subgrade  may  be  flat,  crowned  or  dished  so  that 


in 

Fig.  43     Typical  End  Sections 

the  lower  bounding  line  of  the  end  section  of  pavement 
may  be  straight,  concave  or  convex  as  shown  in  Fig.  43, 
in  which  d  equals  depth  of  pavemert  at  sides,  w  equals 
width,  c  equals  total  crown  and  c'  equals  regular  or  dished 
crown,  as  the  case  may  be,  of  underlying  course  or  sub- 
grade. 

If  the  crown  of  the  pavement  is  the  same  as  that  of  the 
underlying  course  or  subgrade,  the  top  and  bottom  lines  of 
the  end  sections  are  parallel  and  the  thickness  of- the  pave- 
ment is,  therefore,  uniform.  In  such  case,  the  end  section 
may  be  considered  as  a  rectangle  with  dimensions  equal  to 


310 


Measurements 


the  width  and  depth  of  pavement.     Its  area  is,  therefore 
the  product  of  width  times  depth  or  w  X  d. 

(b)  In  Case  I,  Fig.  43,  the  end  section  area  is  equal  to 
the  area  of  the  rectangle  w  x  d  plus  the  area  of  the  crown 
section,  having  a  maximum  depth  of  c.  In  Case  II  the  end 


Fig. 


12  16  20  24  28  32  36 

WIDTH  OF  ROAD,  FEET 

•  ">    d  H>i 
44a    Areas  of  End  Sections  of  Uniform  Thickness 


section  area  is  equal  to  the  area  of  the  rectangle  w  X  d, 
plus  the  crown  section  area,  with  a  maximum  depth  of  c, 
minus  the  crown  section  area  with  a  maximum  depth  of 
c'.  It  is,  -of  course,  evident  that  if  in  this  case  both  crown 
sections  are  equal  (§  360a)  the  end  section  area  is  equal  to 
the  rectangle  w  x  d.  In  Case  III,  the  end  section  area  is 


Measurements  of  Area  311 

equal  to  the  area  of  the  rectangle  w  X  d  plus  the  crown 
section  area  with  a  maximum  depth  of  c,  plus  the  crown 
section  area  with  a  maximum  depth  of  c'. 

(c)  Figs.   44a   and  446  show  the   end   section   areas  for 
.various  uniform  thicknesses  of  different  widths  of  pave- 


x: 


$2-1.6 


2.8 


2.6 


2.4  u 

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2.2  o 


2.0 


1.8 


12 


1G  20  24 

WIDTH  OF  ROAD,   FEET 


32 


1.4 


Fig.  44i    Areas  of  End  Sections  of  Uniform  Thickness 

ment  which  may  be  considered  as  represented  by  the  rect- 
angular area  of  Fig.  43.  The  use  of  these  figures  in  quickly 
ascertaining  end  section  areas  is  illustrated  by  the  following 
examples : 


312  Measurements 

Case  I.   Width  of  pavement  20  feet,  thickness  of  sides  6  inches, 
crown  2  inches  parabolic,  subgrade  flat. 
Area  of  rectangle,  Fig.  44a      =  1.11    sq.  yds. 
Area  of  crown  section,  Fig.  42  =     .247    "      " 
Total  area,  end  section  =  1.357    "      " 

Case  II.  Width  of  pavement  30  feet,  thickness  at  sides  3  inches,  upper 
crown  4  inches  straight  line,  lower  crown  3  inches  straight' 
line. 

Area  of  rectangle,  Fig.  44a  =    .833  sq.  yds. 

Area  of  upper  crown  section,  Fig.  42=  .555  "  " 
Sum  of  areas  =  1.388  "  " 

Area  of  lower  crown  section,  Fig.  42  =  .415  "  " 
Difference,  total  area  end  section  =  .973  "  " 

Case  III.  Width  of  pavement  16  feet,  thickness  at  sides  5  inches,  upper 
crown  4  inches  circular  arc,  lower  dished  crown  3  inches 
straight  line. 

Area  of  rectangle,  Fig.  44a  =    .74    sq.  yds. 

Area  of  upper  crown  section,  Fig.  42=  .395  "  " 
Area  of  lower  crown  section,  Fig.  42  =  .222  "  " 
Total  area  end  section  =  1.357  "  " 

If  it  is  desired  to  obtain  end  section  areas  in  square  feet, 
rather  than  in  square  yards,  the  values  shown  in  Figs.  42 
and  44  should  be  multiplied  by  9  (§  2296). 


MEASUREMENTS  OF  VOLUME 

361.  Volumes  Computed  from  End  Section  Areas.  The 
common  unit  of  volume  measurement  for  pavement  proper 
as  well  as  for  most  materials  used  in  highway  construction, 
with  the  exception  of  bituminous  materials,  is  the  cubic 
yard.  The  number  of  cubic  yards  of  finished  pavement  is, 
for  any  unit  length,  most  conveniently  ascertained  from 
the  end  section  area  (§  360) .  Where  the  relation  between 
uncompacted  and  compacted  material  is  known,  this  method 
is  also  useful  in  checking  quantities  of  various  materials 
placed  on  the  road.  Volumes  in  cubic  yards  per  linear  foot 
of  pavement  with  end  section  areas  up  to  4  square  yards 
are  shown  in  Fig.  45,  which  will  be  found  useful  to  the 
Inspector  in  checking  his  other  measurements. 


Measurements  of  Volume 


313 


362.  Volumes  Measured  in  Excavation.  Quantities  of 
materials  are  sometimes  measured  in  excavation  by  taking 
cross-section  levels  at  suitable  intervals  and  computing 


4.0 


gl.O 

CL 

to 

Q 

oc 


ol.l 

m 

=3 
O 


1.2 


1.3 


AREA  END  SECTION  SQ.  YDS. 
3.5  3.0  2.5  2.0 


2E7 


0  0.5  1.0  1-5 

AREA  END  SECTION  SQ.  YDS. 


.3  o 

CO 


2.0 


Fig.  45     Volumes  per  Linear  Foot  Represented  by  Various  End 
Section  Areas 

volumes  from  the  end  areas.  Such  measurements  and  com- 
putations are  ordinarily  made  by  the  Engineer  and  not  by 
the  Inspector. 


314  Measurements 

363.  Capacities  of  Rectangular  Containers.    The  capac- 
ity of  a  rectangular  container  is  the  product  obtained  by 
multiplying  together  the  inside  dimensions  of  length,  width 
and   height.     For   computing  volumes   in   cubic  yards   or 
cubic  feet,  measurements  are  most  conveniently  made  with 
a  tape  or  rule  graduated  in  feet  and  decimal  parts  of  a  foot 
rather  than  in  feet  and  inches. 

364.  Contents  of  Wagons  and  Barrows,   (a)  For  accurate 
volume  measurements  the   contents  of  wagons  or  barrows 
should  be  struck  as  nearly  level   as  possible.     If  material 
is    to    be   measured    by  wheelbarrow   loads    of   fixed   vol- 
ume, the  volume  should  be  gauged  by  measuring  the  ma- 
terial into  the  barrow  by  means  of  a  cubic  foot  box  and 
marking  the  level  attained   by  such  volume.    The  volume 
of  material  delivered  by  wagon  or  truck  is  ordinarily  ascer- 
tained by  computing  the  volume  of  a  geometrical  solid  with 
plane  surfaces,  having,  in  general,  the  same  dimensions  of 
length  and  width  as  the  inside  dimensions  of  the  wagon 
and  a  height,   depending  upon  the  extent   to  which  the 
wagon  is  filled.    If  the  bottom  of  the  wagon  is  flat  and  the 
top  of  the  load  is  properly  leveled  the  geometrical  figure 
will  ordinarily  be  a  rectangular  prism  or  a  prismoid,  or  a 
combination  of  such  figures,  whose  volumes  may  be  com- 
puted separately  and  then  added  together. 

(6)  If  the  area  of  either  the  upper  or  lower  face  of  a 
rectangular  prism  is  denoted  as  A  and  the  height  as  h, 
then  the  volume  of  the  prism  is  ascertained  by  multiplying 
A  by  h.  Thus,  if  V  represents  volume,  V  =  Ah.  In  the 
prism  opposite  faces  are  not  only  parallel  but  of  the  same 
dimensions.  In  the  prismoid,  however,  only  two  faces  need 
be  parallel  and  these  parallel  faces  may  be  of  different 
dimensions.  If  the  parallel  faces  are  at  the  top  and  bot- 
tom and  their  respective  areas  are  denoted  as  A  and  a 
and  the  vertical  distance  between,  or  the  height  as  h,  then 


Measurements  of  Volume 


315 


In  this  formula  m  denotes  the  area  of  a  section  midway  be- 
tween and  parallel  to  the  top  and  bottom.  If  both  top  and 
bottom  are  rectangles  then  area  w  is  a  rectangle  with  di- 
mensions which  are  the  mean  of  those  for  top  and  bottom. 
(c)  As  an  example  suppose  it  is  desired  to  ascertain  the 
loaded  contents  of  a  flat-bottom  wagon  with  side  and  end 


0.3' 


.gtas^M.            'w&>»^     V    ^tffm                   W%??^ 

l\ 

ii 

X 

05' 

ii                7 

i 

4 

i 

i 

£      34'      > 

<                             5  8  '                           >1 

4,5' 

6.2'  * 

Fig.  46     Example  of  Volume  Contents  of  Loaded  Wagon 

sections  as  shown  in  Fig.  46  and  the  load  above  the  sides 
indicated  in  the  shaded  portion  roughly  leveled  to  a  rect- 
angular surface.  It  is  evident  that  the  geometrical  solid 
represented  by  the  load  is  composed  of  rectangular  prism 
I,  prismoid  II  and  prismoid  III.  The  volume  of  these  figures 
is  determined  as  follows: 

I.   Rectangular  Prism: 

V  =  3.4  x  5.8  X  2.0  =  39.44  cu.  ft. 
II.   Prismoid: 


V  =  ^[(3.4  X  5.8)  +  (4.5  X  6.2)  + 


1.4  +4.5      5.8  +  6.: 

n  '    X  c\ 


=  11.87  cu.  ft. 


III.   Prismoid: 
V  -  ^[(4.5  X  6.2)  +  (2  X  3)  + 


4.5  +  2.0      6.2  +  3 


5.83  cu.  ft. 


316  Measurements 

The  total  volume  is  then  39.44  -f-  11.87  +  5.83  =  57.1    cu. 
ft.  or  *%f  =  2.1  cu.  yds. 

365.  Capacity  of  Tanks,  (a)  Tanks  for  storing  or  heat- 
ing bituminous  materials  are,  in  the  main,  either  cylindrical 
or  rectangular.  Cylindrical  tanks  may  have  flat,  or  partly 
spherical  ends  or  bottoms,  as  the  case  may  be,  and  rect- 
angular tanks  may  have  flat  or  partly  cylindrical  bottoms. 
In  measuring  the  volume  contents  of  tanks  proper,  allow- 
ance should  be  made  for  the  space  occupied  by  steam  coils, 
agitators  or  other  equipment  which  may  be  immersed  or 
partly  immersed  in  the  material. 

(b)  The  volume  of  material,  in  a  cylinder  standing  on  end, 
is  equal  to  the  inside  area  of  the  circular  bottom  multiplied 
by  the  height  or  depth  of  material.    The  area  of  any  circle 
is  equal  to  0.7854  times  the  square  of  the  diameter.    Thus,  if 
the  inside  diameter  of  a  tank  is  4  feet  and  the  depth  of 
material  in  the  tank  is  6  feet,  the  volume  of  material  is  equal 
to    0.7854(4  x  4)  x  6  =  75.398    cubic    feet  =  75.398  x  7.48 
=  563.98  gallons.  (§369.) 

(c)  The  volume  of  material,  in  a  cylinder  lying  horizon- 
tally on  its  side,  is  equal  to  the  inside  length  of  the  cylinder 
times  the  inside  area  of  the  circular  end,  if  the  cylinder  is 
filled.     If  it  is  partially  filled,  then  the  volume  is  equal  to 
the  length  times  the  area  of  the  segment  of  a  circle  repre- 
sented by  the  end  section  of  the  material.    If  the  height  of 
liquid  is  calculated  as  a  decimal  fraction  of  the  diameter 
of  the  circle,  the  diagram  shown  in  Fig.  47  may  be  used  to 
obtain  a  factor  which  in  the  following  formula  will  give  the 
volume  in  gallons  of  material. 

V  =  7ASFl  x  D2  X  L. 

In  this  formula  V  equals  volume  in  gallons,  D  equals  di- 
ameter of  cylinder  in  feet,  L  equals  length  of  cylinder  in 
feet,  and  F±  equals  factor  obtained  from  Fig.  47. 

(d)  Many  horizontal  cylindrical  tanks  have  partly  spheri- 
cal or  bumped  ends,  the  radius  of  the  bump  being  the  same 


Measurements  of  Volume 


317 


as  the  diameter  of  the  tank.  Accurate  calculation  of  volume 
contents  then  becomes  more  complicated  but  a  rapid  method 
has  been  developed  by  Howell,1  in  which  certain  factors  are 

HEIGHT  OF  LIQUID  EXPRESSED  AS  FRACTION  OF  DIAMETER 
,50 .60  .70  .80  .90  1.00 


.70 


'.50 


.40 


.40 


.30 


.10 


HEIGHT  OF'UQUID  EXPRESSED  AS  FRACTION  OF  DIAMETER 

Fig.  47     Factor  Fj  for  Calculating  Contents  of  Cylindrical  Tanks 

obtained  from  curves  shown  in  Figs.  47  and  48.    To  obtain 

the  factors  from  these  curves  it  is  first  necessary  to  ascertain 

the  height  of  material  as  a  decimal  fraction  of  the  diameter 

1  Jour,  of  Industrial  &  Engineering  Chemistry,  May,  1916,  p.  430. 


318 


Measurements 


of  the  tank.     The  following  formula  is  then  used  to  com- 
pute the  volume  in  gallons  of  material. 

V  =  7ASD2(LFl  +  2DF2). 

In  this  formula  V  equals  volume  in  gallons,  D  equals  di- 
ameter of  cylinder  in  feet,  L  equals  length  of  cylinder  in 

HEIGHT  OF  LIQUID  EXPRESSED  AS  FRACTION  OF  DIAMETER 

.50  .60  .70  .80  .90  1.00 

.06 


'.04 


.03 


.02 


0  .10  .20  .30  .40  .50 

HEIGHT  OF  LIQUID  EXPRESSED  AS  FRACTION  OF  DIAMETER 

Fig.  48    Factor  F2  for  Calculating  Contents  of  Cylindrical  Tanks 

feet,  FI  equals  factor  obtained  from  Fig.  47,  and  F2  equals 
factor  obtained  from  Fig.  48.  As  an  example,  suppose  the  in- 
side diameter  of  a  tank  is  4  feet,  its  cylinder  length  10  feet 
and  that  the  height  of  liquid  is  3  feet.  The  height  of  liquid 
is  then  J  or  0.75  of  the  diameter.  From  this  value  in  Fig.  47 
0.63  is  obtained  as  factor  FI,  and  in  Fig.  48  '0.047  is  obtained 
as  factor  F2.  Using  these  factors  in  the  above  formula,  we 


Measurement  of  Volume  319 

have  V  =  7.48  X  (4  x  4)[(10  x  0.63)  +  (2  x  4  x  0.047)]  = 
798.98  gallons. 

(e)  A  rectangular  tank  with  semi-cylindrical  bottom  has 
an  end  section  composed  of  a  rectangle,  and  a  semicircle 
with  the  same  diameter  as  the  width  of  the  tank.  If  the 
height  of  liquid  in  such  a  tank  is  above  the  cylindrical  por- 
tion, the  volume  in  gallons  may  be  expressed  by  the  follow- 
ing formula  in  which  V  equals  volume  in  gallons,  D  equals 
width  of  tank  in  feet,  L  equals  length  of  tank  in  feet  and 
H  equals  total  height  of  liquid  in  feet. 

V  =  7.48[0.3927D2  +  DL(H  -  Z))]. 

If  the  height  of  liquid  is  within  the  cylindrical  portion  then 
the  end  section  is  a  segment  of  a  circle,  and  its  volume  may 
be  determined  by  the  first  formula  in  the  preceding  para- 
graph (§  365c)  by  first  calculating  the  height  of  liquid  as  a 
decimal  fraction  of  the  diameter  of  the  circle  (width  of  tank) 
and  obtaining  the  proper  factor  from  Fig.  47. 

366.  Volumes  Computed  from  Weight,  (a)  The  actual 
volume  of  a  material  may  be  computed  from  its  weight  pro- 
vided its  specific  gravity  is  known.  This  is  done  by  divid- 
ing its  weight  by  the  product  obtained  from  multiplying  a 
unit  volume  of  water  (§  370)  by  the  specific  gravity  of  the 
material.  Thus,  if  it  is  desired  to  ascertain  the  number  of 
gallons  represented  by  500  pounds  of  tar  with  specific 
gravity  of  1.24,  first  multiply  the  weight  of  a  gallon  of  water, 
8.34  pounds,  by  1.24  and  divide  500  pounds  by  this  product 
as  follows: 

- 


(6)  Certain  products,  such  as  broken  stone,  gravel,  sand, 
etc.,  occupy  an  apparent  volume  which  is  different  from 
their  actual  volume.  This  is  due  to  the  fact  that  unoccupied 
space  or  voids  exist  between  the  individual  fragments.  The 
actual  volume  of  these  products  is  determined  in  the  same 
manner  as  described  in  the  preceding  paragraph,  but  in 


320  Measurements 

order  to  determine  the  apparent  volume  it  is  necessary  to 
know  the  per  cent  of  voids.  If  this  is  known,  the  apparent 
volume  then  equals  the  actual  volume  multiplied  by  100 
and  divided  by  100  minus  the  per  cent  of  voids.  Thus,  if 
the  actual  volume  is  1  cubic  yard  and  the  per  cent  of  voids 
is  40,  the  apparent  volume  is 

100 
100^40  =  1.66  cubic  yards. 

MEASUREMENT  BY  WEIGHT 

367.  Weights  Computed  from  Volume,     (a)  "The  compu- 
tation of  weight  from  volume  involves  the  specific  gravity 
of  the  material  under  consideration.    Weight  is  determined 
from   actual   volume   by  multiplying  the   volume   by   the 
weight  of  a  unit  volume  of  water  (§  370)  and  multiplying 
this  product  by  the  specific  gravity  of  the  material.    Thus, 
if  it  is  desired  to  ascertain  the  weight  of  2000  gallons  of 
asphalt  with  a  .specific  gravity  of  1.04,  the  following  result 
is  obtained: 

2000  x  8.34  x  1.04  =  17,347  pounds  =  8.674  tons. 

(6)  If  the  determination  involves  apparent  volume 
(§  3666)  then  the  voids  in  such  volume  must  be  taken  into 
account  in  computing  weight.  Actual  volume  equals  the 
apparent  volume  divided  by  100  and  multiplied  by  100 
minus  the  per  cent  of  voids.  Thus,  40  cubic  yards  of  broken 
stone  with  45  per  cent  voids  equals 

T4A  X  (100  -  45)  =  22  cubic  yards  of  solid  rock. 

368.  Direct   Determination   of  Weight,     (a)  The   direct 
determination  of  weight,   by  means  of  balance  or  scales, 
usually  involves  the  weight  of  a  container,   so  that  two 
weighings    are    necessary,    that    of    the    empty    container, 
known  as  the  tare  weight,  and  that  of  the  container  filled 
or  partly  filled,  known  as  gross  weight.     The  weight  of 
material  is  the  difference  between  gross  and  tare.     If  the 


Equivalent  Measures 


321 


same  weight  of  container  is  used  in  a  series  of  weighings, 
the  tare  becomes  a  constant,  which  need  not  be  determined 
but  once,  except  that  it  should  be  checked  from  time  to 
time.  Some  scales  are  furnished  with  two  beams  in  which 
case  the  tare  weight  may  be  set  on  one  of  the  beams  and 
the  other  used  to  directly  ascertain  the  weight  of  material. 
The  use  of  such  scales  eliminates  the  necessity  of  subtraction. 
(6)  The  accuracy  of  a  weighing  device  may  be  tested  by 
weighing  a  known  volume  of  water  having,  if  possible,  a 
calculated  weight  within  the  range  of  weighings  which  are 
to  be  made.  The  sensitiveness  of  the  device  may  be  tested 
by  adding  to,  or  subtracting  from,  such  volume  smaller 
known  volumes  of  water,  about  T^7  and  roW  °f  the  original 
volume  and  noting  the  difference  in  scale  readings. 

EQUIVALENT  MEASURES 

369.  Common  Measures.  The  following  equivalents  of 
common  measure  may  be  useful  to  the  Highway  Inspector. 
The  decimal  parts  of  a  foot  represented  by  from  0  to  12 
inches  is  shown  in  Fig.  49 

MEASURES  OF  LENGTH 


Miles 

Yards 

Feet 

Inches 

1  = 

1760  = 

5280 

1  = 

3    = 

36 

.0333  = 

1    = 

12 

.0833    = 

1 

MEASURES  OF  SURFACE 


Square 
Yards 

Square 
Feet 

Square 
Inches 

1  =                       9  = 

1296 

0.111  = 

1  = 

144 

0.007  = 

f 

322 


Measurements 


l.OLJ— U 


.INCHES 
7 8 9  10  11  12 


0123456 

INCHES 

Fig.  49     Equivalents  of  Inches  in  Decimal  Parts  of  a  Foot 


MEASURES  OF  VOLUME 


Cubic 

Cubic 

Cubic 

U.S. 

U.S. 

Yards 

Feet 

Inches 

Gallons 

Bushels 

1  = 

27  = 

46,656  = 

20.20 

.03704  = 

1  = 

1728  = 

7.48 

1  = 

0.0043 

0.0046=   - 

0.1337  = 

231  = 

1  = 

0.176 

1.2445  = 

2150.5  = 

9.31  = 

1 

Equivalent  Measures 

MEASURES  OF  WEIGHT 


323 


Long  Tons 

Tons 

Pounds 

Ounces 

Kilograms 

Grams 

1  = 

1.12  = 

2240 

1  = 

2000 

0.0005  = 

1  = 

16  = 

0.4536  = 

453.6 

1  = 

28.35 

2.205  = 

35.274  = 

1  = 

1000 

370.  Weight  of  Water.  The  weight  of  water  is  ordinarily 
considered  at  its  point  of  maximum  density  4°  C.  (39°  F.). 
Owing  to  the  fact  that  it  expands  with  increase  in  tempera- 
ture, the  weight  of  any  volume  at  a  higher  temperature  will 
be  lower  than  the  weight  of  the  same  volume  at  39°  F.  At 
a  temperature  of  60°  F.  its  weight  will  be  about  0.1  per 
cent  less,  and  at  75°  F.  about  0.3  per  cent  less  than  at  39°  F. 
These  differences  are  so  small  that  they  are  ordinarily 
neglected  in  computations  of  volume  and  weight  relations 
as  based  upon  the  specific  gravity  of  other  material  at  nor- 
mal temperature.  The  weights  of  various  unit  volumes  of 
water,  and  the  volume  equivalents  of  1  pound  of  water,  are 
as  follows: 


1           cubic  inch     = 
27.68      cubic  inches  = 
1           cubic  foot      = 
0.016    cubic    " 
1          gallon 
0.1198  gallon 

0.0361  pound 
1           pound 
62.43      pounds 
1           pound 
8.31:5    pounds 
1           pound 

1  cubic  yard     =  1685.6        pounds 


CHAPTER  XVII 

MISCELLANEOUS    FIELD    TESTING   AND 
SAMPLING  EQUIPMENT 

TESTS   OF  MINERAL  AGGREGATES 

371.  Mechanical  Analysis  and  Grading,  (a)  For  making 
mechanical  analyses  or  grading  determinations  the  Inspector 
should  be  provided  with  a  suitable  set  of  screens  and  sieves 
and  a  weighing  device.  Ordinary  laboratory  apparatus  is 
too  cumbersome  for  convenient  field  use  and  the  following 
outfit  shown  in  Fig.  50  has,  therefore,  been  devised  for  this 
purpose.  A  single  screen  frame  is  used  for  all  screens. 
This  frame  is  composed  of  two  circular  brass  rims  about  2 
inches  high,  one  fitting  snugly  within  the  other.  The  outer 
rim  has  a  diameter  of  8  inches  and  carries  a  narrow  shoulder 
around  the  inside  of  the  lower  edge.  The  screen  plates  are 
thin  circular  disks  7yf  inches  in  diameter  which  fit  inside  of 
the  outer  rim  and  are  clamped  against  the  shoulder  by 
means  of  the  inner  rim.  The  screens  consist  of  brass  plates 
2^  inch  thick,  with  punched  circular  holes.  Sieves  may 
consist  of  flat  brass  rings  to  which  the  wire  mesh  is  perma- 
nently fastened  although  a  set  of  small  nestable  sieves  may 
be  found  more  convenient.  Two  spring  balances  are  used 
with  the  outfit.  One  of  these  balances  for  weighing  frag- 
ments larger  than  J  inch  in  diameter  has  a  capacity  of  30 
pounds  with  scale  divisions  of  TV  pound  and  an  adjustable 
pointer  which  may  be  set  at  zero  before  a  weighing  is  to 
be  made.  With  this  balance  weighings  are  made  in  a  cloth 
bag  which  is  attached  to  the  hook.  A  more  delicate  bal- 
ance for  weighing  material  smaller  than  J  inch  in  diameter 

324 


Tests  of  Mineral  Aggregates  325 

has  a  capacity  of  200  grams  with  scale  divisions  of  1  gram, 
and  carries  a  small  pan  in  which  the  material  is  weighed. 
A  light  camera  tripod  will  be  found "  convenient  for  sup- 
porting the  balances  when  in  use,  but  is  not  absolutely 


iWr  '*vr 

Fig.  50     Field  Outfit  for  Mechanical  Analysis 

necessary.  A  complete  outfit  including  all  screens  and  sieve 
plates,  as  well  as  a  tripod,  weighs  approximately  10  pounds 
and  may  be  packed  in  a  rectangular  space  6x8x17  inches. 
The  weight  of  outfit  may  ordinarily  be  reduced  two  or  three 
pounds  by  selecting  only  those  plates  which  will  be  needed 
for  a  particular  job. 

(6)  For  testing  purposes  a  sample  may  be  considered  as 
consisting  of  coarse  or  fine  material,  depending  upon  whether 
it  will  practically  all  be  retained  upon,  or  will  pass  a  i-inch 
screen.  If  there  is  a  substantial  proportion  of  both  sizes, 


326        Testing  and  Sampling  Equipment 

as  in  the  case  of  bank  gravel,  it  is  considered  as  being  a 
mixture  of  coarse  and  fine  material.  A  description  of  the 
method  of  testing  such  a  sample  will  also  illustrate  the 
procedure  which  should  be  followed  for  either  coarse  or  fine 
material  alone,  it  being  understood  that  the  particular 
screens  or  sieves  used  will  depend  upon  specification  re- 
quirements, or  the  purpose  for  which  the  material  is  to  be 
used.  Standard  screens  have  circular  openings  of  3|,  3, 
2J,  2,  1J,  1,  f,  |,  and  J  inches  diameter.  Standard  sieves 
have  the  following  number  of  meshes  per  linear  inch:  10, 
20,  30,  40,  50,  80,  100  and  200.  A  sample  of  coarse  material 
should  weigh  at  least  50  times  the  weight  of  the  largest 
fragment  present,  and  a  sample  of  fine  material  should 
weigh  at  least  100  grams.  All  samples  should  be  air  dry 
before  testing  and  should  be  screened,  over  a  large  piece  of 
manila  paper,  in  a  place  free  from  air  currents  which  may 
carry  off  the  fine  material. 

(c)  The  method  is  as  follows:  Suspend  the  large  spring 
balance  from,  the  tripod,  or  any  rigid  support,  so  that  a 
small  canvas  bag  may  swing  freely  from  its  lower  end.  Hang 
the  bag  on  the  hook  and  adjust  the  pointer  to  zero  on  the 
scale.  Weigh  out  exactly  10  pounds  of  the  material,  which 
is  indicated  by  one  complete  revolution  of  the  pointer. 
Then  pass  the  material  through  the  largest  screen  required 
and  weigh  the  amount  retained,  each  TV  pound  being  re- 
corded as  1  per  cent.  Do  the  same  with  the  next  largest 
screen,  and  so  on  down  to  the  J-inch  screen.  If  the  maxi- 
mum size  of  fragment  necessitates  more  than  a  10-pound 
sample,  set  aside  the  material  which  passes  the  J-inch  screen 
and  repeat  the  entire  operation  with  as  many  10-pound  lots 
as  may  be  necessary.  Then  thoroughly  mix  all  of  the  ma- 
terial which  has  passed  the  J  inch  and  weigh  it.  Substitute 
the  small  spring  balance  for  the  large  and  weigh  out,  if  possi- 
ble, exactly  200  or  100  grams  of  the  fine  material.  Pass  this 
sample  through  the  largest  sieve  required  and  weigh  the 
amount  retained.  Each  2  grams  should  be  recorded  as  1 


Tests  of  Mineral  Aggregates 


327 


per  cent  of  the  fine  material,  if  the  original  sample  weighed 
200  grams,  or  each  gram  as  1  per  cent,  if  the  original  sample 
weighed  100  grams.  If  a  smaller  weight  is  necessary  the 
per  cent  retained  should  be  calculated.  Do  the  same  with 
the  next  largest  sieve,  and  so  on  down  to  the  smallest.  If 
desired  the  material  passing  the  smallest  may  also  be  weighed 
as  a  check  upon  the  accuracy  of  the  other  weighings.  All 
weighings  of  fine  material  should  finally  be  calculated  as  per 
cent  of  the  original  sample. 

(d)  The  entire  operation  of  recording  results  is  illustrated 
by  the  following  example,  which  represents  the  mechanical 
analysis  of  an  original  20-pound  sample  of  gravel.  The  opera- 
tion has  been  conducted  upon  two  portions  of  10  pounds 
each,  which  is  the  most  convenient  amount  to  use.  It 
should  be  noted,  however,  that  the  capacity  of  the  large 
spring  balance  will  allow  for  either  a  20-  or  30-pound  sample. 
In  the  former  case,  each  T%  pound,  and  in  the  latter,  each 
T%  pound  represents  1  per  cent  of  the  sample. 


Operation 

a) 
H>.    % 

(2) 
H>.      % 

Average 

% 

\Veight  of  sample 

10 

10 

Ret  on  2-inch  screen 

0.6  =    6 

0.2  =    2 

4 

Pass.  2  in.,  ret.  on  1-in.  screen.  .  .  . 

«        -I      it       it       it     i     u           .; 

2.0  =  20 
3.2  =  32 

3.0  =  30 
3.8  =  38 

25 
35 

Total  passing  i-inch  screen  

4.2  =  42 

3.0  =  30 

*36 

Grams    % 

*Factor 

% 
Original 
Material 

Weight    of    sample    passing    i-in. 
screen                                    

200 

Ret.  on  10-inesh  sieve  
Pass.    10-mesh,   ret.   on  200-mesh 

48  =  24 
112  =  56 

X.36 
X.36 

9 
20 

Passing  200-m6sh  sieve      

40  =  20 

X.36 

7 

328        Testing  and  Sampling  Equipment 

-  for    COMPLETE  ANALYSIS 

Per  cent 
Retained  on  2-inch  screen. .  .  . v.T.*j. ;  .ir».:.t.rlVi-V.1.i .V.'. '!':>. rtl'>--       4 

Passing  2  inch,  retained  on  1-inch  screen. ..... .,?lfwrr^  .(.){>].  •(»•      25 

Passing  1  inch,  retained  on  |-mch  screen. .  .  ; . . '  '  ! . ! ."!.. . .  . . .         35 

Passing  j-inch  screen,  retained  on  10-mesh  sieve.  .  r'.Vl'.-ll^.  .'''•*•       9 
Passing  10  mesh,  retained  on  200-mesh  sieve.  ./,(.-.  .,V.JKX^-{-  •]•/ -\.  20 

Passing  200-mesh  sieve , 7 

Total  100 

372.  Organic  Matter  in  Sand,     (a)  The  following  field 
method   for  determining  the   existence  of  harmful  organic 
impurities  in  sand,  for  use  in  cement  concrete,  has  been 
developed  by  Committee  C-9  l  of  the  American  Society  for 
Testing  Materials.     For  this  test  it  is  necessary  to  have  a 
12-ounce  graduated  prescription  bottle  and  a  supply  of  3 
per  cent  solution  of  sodium  hydroxide.     This  solution  may 
be  prepared  by  dissolving  28.5  gKams   (f  oz.  apothecaries' 
weight)   of  sodium  hydroxide  in  a  quart  of  water.     Solid 
sodium  hydroxide  in  the  form  of  sticks  may  be  obtained 
at  any  drug  store  and  should  be  kept  in  a  tightly  corked 
bottle.    It  is  the  most  concentrated  form  of  lye  and  should 
be  handled  with  care  to  prevent  burning  the  skin. 

(6)  To  make  a  test  "fill  a  12-oz.  graduated  prescription 
bottle  to  the  4|-oz.  mark  with  the  sand  to  be  tested.  Add 
a  3-per-cent  solution  of  sodium  hydroxide  until  the  volume 
of  sand  and  solution  after  shaking  amounts  to  7  oz.  Shake 
thoroughly  and  let  stand  over  night.  Observe  the  color  of 
the  clear  supernatant  liquid.  If  this  liquid  is  colorless,  or 
has  a  light  yellow  color,  the  sand  may  be  considered  satis- 
factory in  so  far  as  organic  impurities  are  concerned.  On 
the  other  hand,  if  a  dark  colored  solution,  ranging  from 
dark  red  to  black,  is  obtained,  the  sand  should  be  rejected 
or  used  only  after  it  has  been  subjected  to  the  usual  mortar 
strength  tests"  (§58). 

373.  Silt  in  Sand.     An  approximate  volumetric  determi- 
nation of  silt  in  sand  may  be  made  by  filling  a  100-cubic- 
centimeter  graduated  glass  cylinder,  to  the  50-c.c.  mark, 

1  Proc.  Am.  Soc.  Test.  Mat.,  Vol.  17-1917,  Part  I,  p.  328. 


Tests  of  Mineral  Aggregates  329 

with  sand  and  adding  sufficient  water  to  reach  the  100-c.c. 
mark.  The  contents  of  the  cylinder  should  then  be  thor- 
oughly shaken  and  allowed  to  settle  until  the  supernatant 
liquid  is  clear  or  nearly  so.  Any  silt  which  is  present  will 
settle  as  a  rather  clearly  denned  layer  of  fine  material  on 
top  of  the  sand.  Each  0.1-c.c.  volume  of  this  layer  repre- 
sents 2  per  cent  of  the  volume  of  sand.  The  per  cent  of  silt 
by  weight  may  vary  from  1  to  2  times  the  per  cent  by  volume. 

374.  Quality  of  Gravel  Pebbles.     A  rough  determination 
of  the  quality  of  pebbles,  in-  a  gravel  product,  may  be  made 
by  sorting  out  and  discarding  from  the  total  material  re- 
tained on  the  f-inch  screen  in  the  mechanical  analysis  de- 
termination (§371)  all  pebbles  which  are  manifestly  soft, 
decomposed  or  partly  disintegrated.    A  geologist's  hammer 
is   then   conveniently  used   in  testing   out  the   apparently 
sound  pebbles.     Those  which  are  readily  broken  or,  when 
broken,   are  found  to  be  composed  of  inferior  sandstone 
should  also  be  discarded.    The  remaining  pebbles  and  frag- 
ments which  are  considered  of  good  quality  should  then  be 
weighed.     The  difference  between  this  weight  and  that  of 
the  total  material  retained  on  the  J-inch  screen  gives  the 
weight  of  inferior  material  which  should  be  calculated  upon 
a  percentage  basis  of  the  total  weight  of  pebbles. 

375.  Weight  per  Cubic  Foot,     (a)  The  weight  per  cubic 
foot  of  such  products  as  broken  stone,  broken  slag,  gravel 
and  sand  may  be  made  in  a  cylindrical,  or  cubical,  measure 
with  a  capacity  of  exactly  one  cubic  foot.     A  convenient 
measure  for  field  use  may  be  made  from  f-inch  poplar.    The 
four  sides   are  exactly  one-foot   square  while  the   bottom 
measures  12f "  x  12f ".    To  prevent  warping,  the  sides  and 
bottom  carry  tongue  and  groove  battings  across  the  grain. 
Sides  and  bottom  may  be  quickly  fastened  together  by 
means  of  slotted  brass  angles  and  screw  projections,   at- 
tached as  shown  in  Fig.  51.     This  measure  weighs  only  6 
pounds  and  when  taken  apart  may  be  packed  in  a  rect- 
angular space  13"  X  13"  x  2J". 


330        Testing  and  Sampling  Equipment 

(6)  The  determination  is  made  by  first  introducing  into 
the  measure  about  £  of  the  total  amount  of  material  re- 
quired, care  being  taken  to  avoid  separation  of  sizes.  The 
material  is  then  shaken  down,  by  rocking  the  measure  from 
side  to  side,  until  no  further  settlement  takes  place.  This 
process  is  repeated  until  the  measure  has  been  filled  to  over- 
flowing, after  which  it  is  struck  level  with  the  top  by  means 
of  a  rule  or  straightedge.  The  contents  of  the  box  may 
then  be  weighed  in  portions  by  means  of  a  large  spring 


Fig.  51     Collapsible  Cubic  Foot  Measure 

balance,  such  as  used  for  mechanical  analysis  (§371).  If, 
however,  large  weighing  scales  are  handy,  it  may  be  more 
convenient  to  weigh  the  measure  before  and  after  filling 
and  to  determine  by  difference  the  weight  of  material  per 
cubic  foot. 

376.  Specific  Gravity,  (a)  When  a  material,  such  as 
broken  stone,  is  homogeneous  in  character,  an  approximate 
determination  of  its  specific  gravity  may  be  made  by  sus- 
pending with  a  fine  thread  a  fragment,  weighing  somewhat 
less  than  200  grams,  to  the  pan  support  of  the  small  spring 
balance  described  under  mechanical  analysis  (§  370) .  The 
weight  of  the  fragment  in  air  is  then  ascertained.  The  frag- 


Tests  of  Mineral  Aggregates  331 

ment  should  next  be  submerged  in  water  and  quickly  weighed 
again,  care  being  taken  that  no  air  bubbles  are  held  against 
its  surface.  If  the  weight  in  air  is  denoted  by  a  and  the 
weight  in  water  by  b,  then  the  specific  gravity  of  the  ma- 
terial is  calculated  by  the  formula 

Sp.  gr. 


a-b 

Such  a  determination  should  be  accurate  to  about  5  units 
in  the  second  decimal. 

(b)  If  the  material  is  non-homogeneous,  as  in  the  case  of 
blast-furnace  slag  or  gravel,  but  is  composed  of  relatively 
coarse  particles,  the  determination  should  be  made  on  a 
10-pound  sample  which  is  placed  in  a  wire  basket  suspended 
from  the  hook  of  the  large  spring  balance  (§  371)  by  means 
of  a  wire.  Such  a  basket  may  readily  be  fashioned  from  a 
piece  of  J-inch  square  mesh  wire,  such  as  may  be  obtained 
at  most  hardware  stores.  A  section  21  inches  square  will 
make  a  basket  7  inches  square  and  7  inches  deep,  by  cutting 
out  a  piece  7  inches  square  from  each  corner,  bending  up 
the  sides  and  wiring  them  together.  A  piece  of  stout  wire 
may  be  made  to  serve  as  a  handle.  The  empty  basket 
should  first  be  weighed  in  air  and  then  submerged  in  a  pail 
of  water  to  a  mark  scratched  on  the  wire  suspending  it.  The 
first  weight  is  called  a  and  the  second  b.  The  basket  should 
then  be  dried  and  approximately  10  pounds  of  the  material 
weighed  into  it.  This  weight  is  called  A.  Sample  and 
basket  are  finally  weighed  in  water,  submerged  to  the  same 
mark  on  the  wire  as  in  the  case  of  the  empty  basket.  This 
weight  is  called  B.  From  these  weights  the  specific  gravity 
of  the  product  is  ascertained  by  means  of  the  following 
formula : 

SP-gr-  -(A-a)-(B-b)' 

Once  weights  a  and  b,  which  are  constants,  have  been  ascer- 
tained, determinations  may  be  made  with  only  two  weighings. 


332        Testing  and  Sampling  Equipment 

(c)  In  the  case  of  fine  aggregates  which  will  pass  a  J-inch 
screen,  the  specific  gravity  determination  is  best  made  by 
weighing  out  exactly  100  grams  of  the  product  on  the  small 
spring     balance     (§  371).      A     100-cubic-centimeter     glass 
cylinder  is  then  filled  with  water  to  the  50-c.c.  mark,  after 
which  the  100-gram  sample  is  introduced  and  stirred  with  a 
piece  of  wire  until  free  from  air  bubbles.     The  water  level 
is  then  read  and  the  total  number  of  centimeters  called  a. 
The  difference  in  cubic  centimeters  between  this  reading 
and  the  first  represents  the  number  of  cubic  centimeters 
occupied  by  the  sample.    Its  specific  gravity  is  then  ascer- 
tained by  means  of  the  following  formula: 

Sp.  gr.  =  --  — 
f.fit'/Hti  v«J  i.Iu-:  $)  ooasiL  a  -  50 

(d)  If  a  non-homogeneous  product  is  composed  of  both 
coarse  and  fine  aggregates,  a  representative  sample  should 
be  screened  on  a  J-inch  screen  and  the  percentage  weights 
retained,    and  passing  should  be  recorded.     The   specific 
gravity  of  the  coarse  product  is  then  determined  by  the 
wire  basket  method  (§  3766)  and  the  specific  gravity  of  the 
fine  product  is  determined  by  means  of  the  cylinder  method 
(§  376c)  .    The  following  formula  may  then  be  used  to  ascer- 
tain the  specific  gravity  of  the  entire  product.     In  this 
formula  W  =  per  cent  of  coarse  material  and  G  its  specific 
gravity;    w  =  per  cent  of  fine  material  and  g  its  specific 
gravity. 


~c~  — 

377.  Voids,  (a)  The  per  cent  of  voids  in  a  mineral  aggre- 
gate may  be  calculated  from  its  weight  per  cubic  foot  (§  375) 
and  specific  gravity  (§  377)  by  means  of  the  following 
formula  in  which  W  =  weight  per  cubic  foot  and  G  =  specific 

gravity  : 

(62.43G  -  W  )  X  100 


%  Voids 


62.43G 


Tests  of  Bituminous  Materials  333 

(6)  In  the  case  of  fine  aggregates,  such  as  sand,  when  it 
may  not  be  convenient  to  make  a  determination  of  weight 
per  cubic  foot,  the  weight  of  100  cubic  centimeters  may  be 
determined  by  the  same  general  method  (§  375) ,  using  a 
100-cubic  centimeter  cylinder  (§  374c)  and  the  small  spring 
balance.  The  following  formula  is  then  used  to  determine 
the  per  cent  of  voids. 

100G  -  W 
%  Voids  = 


TESTS   OF  BITUMINOUS  MATERIALS 

378.  Penetration  Test  for  Asphalt  Cements,  (a)  The 
paving  plant  Inspector  should  be  provided  with  the  neces- 
sary apparatus  for  making  penetration  tests  on  asphalt 
cements  which  are  to  be  used  in  asphaltic  concrete  or  sheet 
asphalt  mixes.  This  apparatus  will  ordinarily  consist  of 
the  following: 

A  penetrometer  complete  with  standard  needle  (Fig.  52). 
A  supply  of  round  tin  boxes  1  2T\  inches  in  diameter  and 

If  inches  deep. 
A  large  metal  kitchen  spoon. 
A  tin  or  enamel  ware  dish  at  least  10  inches  in  diameter 

and  3  inches  deep. 
A  1-quart  tin  cup,  iron  tripod  and  alcohol  burner,  for 

heating  water  if  necessary. 
A  thermometer  reading  from  0°  C.  to  110°  C. 

(6)  There  are  a  number  of  makes  of  penetration  machines, 
all  of  which  work  on  the  same  general  principle  and  give 
equivalent  results.  The  New  York  Testing  Laboratory 
penetrometer,  miniature  size,  is  shown  in  Fig.  52.  Briefly 
described,  it  consists  of  a  rod  holding  the  standard  needle 
in  a  vertical  position  and  weighted  to  100  grams.  This  is 

1  This  requirement  is  fulfilled  by  the  American  Can  Company's 
gill  style  ointment  box,  deep  pattern,  3-oz.  capacity. 


334        Testing  and  Sampling  Equipment 

held  in  a  loose  fitting  vertical  sleeve  or  collar,  by  means  of 
a  spring  plunger  or  clamp  which  is  released  by  pressing  the 
large  knob,  shown  midway  between  the  dial  and  needle. 
The  dial  is  divided  into  360  degrees,  each  of  which  repre- 
sents 1  penetration  unit,  or  TV  millimeter  vertical  move- 
ment of  a  sliding  gauge  rod,  which  may  be  raised  or  lowered 
to  make  contact  with  the  rod  holding  the  needle.  At  the 


Fig.  52     New  York  Testing  Laboratory 
Miniature  Penetrometer 

back  of  the  dial  a  pin  and  spring  device  allows  the  pointer 
to  be  set  at  zero  for  any  position  of  the  gauge  rod. 

(c)  The  object  of  the  penetration  test  is  to  ascertain  the 
consistency  of  an  asphalt  cement  by  determining  the  dis- 
tance that  a  standard  needle  weighted  with  100  grams  will 
penetrate  into  it  during  5  seconds,  when  its  temperature  is 
exactly  25°  C.  (77°  F.).  The  standard  needle  should  be 
handled  with  care  and  frequently  examined  to  see  if  its 
point  has  become  blunted  or  turned,  in  which  case  it  should 
be  discarded  and  a  new  needle  secured  from  the  laboratory. 
When  not  in  use  its  point  should  be  protected  by  sticking 
it  into  a  soft  cork.  The  test  specimen  of  asphalt  cement 


Tests  of  Bituminous  Materials  335 

should  be  carefully  prepared  so  that  it  is  not  hardened, 
through  loss  by  volatilization,  during  its  preparation.  If 
the  original  sample  has  not  been  taken  in  a  fluid  condition 
from  the  melting  kettle,  it  should  be  completely  melted  at 
as  low  a  temperature  as  possible  and  stirred  until  homo- 
geneous and  free  from  air  bubbles.  It  should  then  be  poured 
into  one  of  the  small  tin  boxes  and  allowed  to  cool  to  air 
temperature,  after  which  box  and  contents  should  be  placed 
under  water,  in  the  large  dish  and  maintained  at  a  tempera- 
ture of  25°  C.  for  not  less  than  30  minutes,  and  perferably 
1  hour.  In  order  to  maintain  a  temperature  of  25°  C.  in 
warm  weather,  it  may  be  necessary  to  add  a  small  amount 
of  cold  well  water  or  ice  water  to  the  contents  of  the  large 
dish  from  tune  to  time,  and  in  cold  weather,  the  addition 
of  hot  water  may  be  required. 

(d)  The  test  is  made  by  placing  the  base  of  the  pene- 
trometer  in  a  level  position  under  water  in  the  large  dish. 
The  box  of  asphalt  cement  is  then  placed  in  a  firm  position 
on  the  base  of  the  machine  directly  under  the  needle,  still 
covered  with  water  at  25°  C.  The  rod  holding  the  needle 
is  then  carefully  lowered  until  the  point  of  the  needle  just 
makes  contact  with  the  surface  of  the  asphalt.  This  can 
best  be  seen  by  having  the  light  so  located  that  the  needle 
will  be  reflected  from  the  surface  of  the  asphalt.  After  thus 
setting  the  needle,  the  gauge  rod  is  brought  in  contact  with 
the  needle  rod,  and  the  pointer  on  the  dial  set  at  zero.  The 
needle  rod  is  then  released  for  five  seconds  by  pressing  the 
spring  plunger.  This  is  most  conveniently  done  by  count- 
ing 11  ticks  of  a  metronome  set  to  beat  J-second  intervals. 
The  needle  should  be  released  at  the  first  count  and  clamped 
at  the  eleventh.  The  depth  of  penetration  is  ascertained 
by  again  bringing  the  gauge  rod  in  contact  with  the  needle 
rod  and  noting  the  reading  on  the  dial.  At  least  three  tests 
should  be  made  at  points  on  the  surface  of  the  sample  not 
less  than  f  inch  from  the  sides  of  the  container  and  not  less 
than  f  inch  apart.  After  each  test  the  needle  should  be 


336         Testing  and  Sampling  Equipment 

carefully  wiped  toward  its  point,  with  a  clean  dry  cloth, 
to  remove  all  adhering  asphalt.  The  reported  penetration 
should  be  the  average  of  at  least  three  tests  whose  values 
should  not  differ  more  than  four  points  between  maximum 
and  minimum. 

379.  Float  Test  for  Tars,  (a)  If  refined  tar  is  used  at  a 
paving  plant,  its  consistency  may  most  conveniently  be 
obtained  by  means  of  the  float  test  which  requires  the 
following  apparatus: 

A  float  test  apparatus  (Fig.  53). 

Two  1-quart,  tin  cups. 

A  large  metal  kitchen  spoon. 

A  kitchen  knife. 

An  iron  tripod  and  alcohol  burner. 

A  stop  watch. 

A  smooth  brass  plate  about  2  inches  square. 

Two  thermometers  reading  from  0°  C.  to  110°  C. 

(6)  The  float  apparatus  shown  in  Fig.  53  consists  of  an 
aluminum  saucer  and  a  conical  brass  collar,  or  mold,  which 
may  be  screwed  into  a  hole  in  the  bottom  of  the  saucer. 
In  order  to  make  quick  check  tests,  it  will  be  found  con- 
venient to  have  two  molds.  In  making  the  test,  a  small 
sample  of  the  tar  is  first  carefully  melted,  by  gently  warm- 
ing it  in  the  metal  spoon,  at  as  low  a  temperature  as  possi- 
ble. It  is  then  poured  into  the  conical  brass  mold,  which 
has  been  placed  with  the  small  end  down  on  the  brass  plate. 
The  plate  may  first  be  very  lightly  greased  with  a  film  of 
vaseline  to  prevent  the  tar  from  adhering  to  it.  The  mold 
is  slightly  more  than  filled  level  with  the  top,  and  after  the 
tar  has  cooled  all  excess  is  removed  by  means  of  the  knife 
which  has  been  warmed  in  the  flame  of  the  burner.  Mold 
and  plate  should  then  be  placed  in  one  of  the  tin  cups  con- 
taining ice  water  maintained  at  5°  C.  and  allowed  to  remain 
in  the  bath  for  at  least  15  minutes.  Meanwhile,  the  other 
cup  is  filled  about  three-fourths  full  of  water,  placed  on  the 


Tests  of  Bitumionus  Materials  337 

tripod  and  heated  to  50°  C.,  which  temperature  is  carefully 
maintained,  to  within  one-half  a  degree,  throughout  the 
test.  After  the  test  specimen  has  been  kept  in  the  ice  water 
for  at  least  15  minutes,  the  mold  is  removed  from  the 
plate  and  screwed  tightly  into  the  saucer,  and  is  then  imme- 
diately floated  in  the  hot  bath.  As  the  plug  of  bituminous 
material  becomes  warm  and  fluid,  it  is  gradually  forced 
upward  and  out  of  the  mold,  until  water  gains  entrance  to 
the  saucer  and  causes  it  to  sink.  The  time  in  seconds  elaps- 
ing between  placing  the  apparatus  on  the  water  and  when 


Fig.  53     New  York  Testing  Laboratory  Float  Apparatus 

the  water  breaks  through  the  tar  is  determined  by  means  of 
a  stop  watch  and  is  reported  as  a  measure  of  the  consistency 
of  the  tar. 

380.  Pat  Test  for  Sheet  Asphalt  Mixtures,  (a)  At  a 
paving  plant  in  which  sheet  asphalt  surface  mixture  is 
being  manufactured,  samples  of  the  hot  mix  are  subjected 
to  the  pat  test,  as  a  guide  in  ascertaining  the  proper  per- 
centage of  asphalt  cement  which  should  be  used.  This  test 
requires  the  following  apparatus: 

A  wooden  paddle  with  blade  about  6  inches  long,  4  inches 
wide  and  J  inch  thick. 


338        Testing  and  Sampling  Equipment 

A  supply  of  unglazed  Manila  wrapping  paper. 
An  ordinary  mason's  trowel  for  sampling. 
An  armored  thermometer  (§  386) . 


Fig.  54    Pat  Stains 

(6)  The  test  is  made  by  taking  a  small  sample  of  the  hot 
mix  from  the  material,  delivered  from  the  mixer,  and  not- 


Tests  of  Bituminous  Materials  339 

ing  the  temperature  of  the  batch  or  load.  The  sample  is 
immediately  placed  upon  a  sheet  of  the  manila  paper,  rest- 
ing upon  a  flat  board  or  bench  top.  The  paper  is  then 
folded  over  the  sample  and  the  flat  of  the  paddle  pressed 
heavily  against  it.  After  compressing  the  sample,  the  paper 
is  struck  a  sharp  blow  with  the  paddle,  then  opened  and 
the  pat  removed.  The  character  of  the  stain  left  upon  the 
paper  is  examined  and,  considered  in  connection  with  the 
temperature  of  the  sample,  indicates  whether  or  not  the 
proper  percentage  of  bitumen  is  present.  Three  classes 
of  stains  obtained  from  pats  taken  at  a  temperature  of 
about  300°  F.  are  shown  in  Fig.  54.  The  lightest  stain  indi- 
cates a  deficiency  of  asphalt  and  the  darkest  an  excess  of 
asphalt.  The  medium  stain  indicates  about  the  proper  per 
cent  of  asphalt.  Considerable  experience  is  necessary  to 
properly  interpret  the  results  obtained  from  the  pat  test, 
and  the  temperature  of  the  material  should  always  be  taken 
into  account.  If  the  proper  per  cent  of  bitumen  is  present, 
stains  which  show  only  the  imprint  of  individual  sand  grains 
indicate  a  deficiency  of  filler  which,  if  present  in  proper 
amount,  will  produce  a  more  uniform  stain. 

381.  Moisture  in  Wood  Block,  (a)  For  checking  the 
amount  of  oil  present  in  creosoted  wood  block  (§  3226)  the 
plant  Inspector  may  be  required  to  determine  the  amount  of 
moisture  in  both  the  treated  and  untreated  wood.  A  fairly 
close  approximation  of  this  factor  may  be  obtained  by  the 
following  method  which  calls  for  the  apparatus  listed  below. 

A  one-half  pint  iron  retort. 

A  bent  glass  condensing  tube  about  30  inches  long  with 

cork  connection  to  the  retort. 
A  separating  funnel,  capacity  120  cubic  centimeters  with 

outlet  graduated  in  fifths  of  a  cubic  centimeter. 
A  balance,1  capacity  100  grams,  sensitive  to  0.1  gram. 

1  If  such  a  balance  is  not  at  hand  the  small  spring  balance  (§371) 
will  be  sufficiently  accurate  for  rough  determinations. 


340        Testing  and  Sampling  Equipment 

Two  iron  stands  with  ring  support  and  two  clamps. 

A  Bunsen  burner  with  rubber  tubing,  or  a  large  alcohol 

burner. 
A  supply  of  water  saturated  xylol.1 

(6)  In  making  the  test,  two  average  cubic  feet  of  un- 
treated block  are  selected  and  both  weighed.    These  weights 


ti; 


Fig.  55     Apparatus  for  Determining  Moisture  in  Cresoted  Wood  Block 

should  be  approximately  the  same.  One  cubic  foot  is  sus- 
pended in  a  wire  cage  in  the  treating  tank  (§  3226)  and  sub- 
jected to  the  regular  treatment  with  creosoting  oil.  The 
other  cubic  foot  is  taken  to  a  wood  drilling  machine  and  a 
large  number  of  borings  made  quickly.  These  borings  should 
be  thoroughly  mixed  and  a  10-gram  sample  taken  and 
rapidly  weighed.  The  sample  is  then  placed  in  the  iron 
retort  and  covered  with  water-saturated  xylol.  The  top  of 

1  Water  saturated  xylol  is  prepared  by  heating  a  mixture  of  xylol 
and  water  with  frequent  shakings  and  then  removing  the  water  by 
means  of  a  separatory  funnel. 


Tests  of  Bituminous  Materials  341 

the  retort  is  then  clamped  on,  using  a  paper  gasket,  and  the 
apparatus  set  up  as  shown  in  Fig.  55,  care  being  taken  to 
secure  a  tight  connection  between  the  retort  and  condens- 
ing tube.  Heat  is  then  gradually  applied  until  all  of  the 
xylol  has  distilled  over  at  the  rate  of  about  2  drops  per 
second.  Moisture  present  in  the  wood  will  be  carried  over 
with  the  xylol  and  upon  standing  will  separate  from  the  dis- 
tillate, in  the  graduated  portion  of  the  funnel  where  its 
volume  in  tenths  of  a  cubic  centimeter  may  be  read  off 
directly  as  per  cent  of  the  original  sample.  After  treat- 
ment the  other  cubic  foot  of  wood  is  first  weighed  and  then 
subjected  to  the  same  test,  the  per  cent  of  water  present 
being  ascertained. 

(c)  The  amount  of  oil  actually  absorbed  is  then  calculated 
as  follows,  where  X  equals  pounds  of  oil  per  cubic  foot  of 
wood,  W  equals  weight  of  untreated  wood,  in  pounds  per 
cubic  foot,  W  equals  weight  of  treated  wood,  in  pounds  per 
cubic  foot,  p  equals  per  cent  of  moisture  in  untreated  wood 
and  pf  equals  per  cent  of  moisture  in  treated  wood. 

W 


Thus  for  example,  suppose  the  weight  per  cubic  foot  of 
untreated  wood  is  50  pounds  and  it  contains  16  per  cent  of 
moisture,  while  the  weight  of  treated  wood  is  60  pounds 
per  cubic  foot  and  it  contains  2  per  cent  of  moisture.  Then 
the  number  of  pounds  of  oil  per  cubic  foot  of  treated  wood  is. 

en  9  v  fin 

60  -  ^  (100  -  16)  -  ^p  -  16.8  pounds. 

382.  Absorption  of  Asphalt  Block.  A  rough  field  test  fox 
determining  the  approximate  absorption  of  asphalt  block 
may  be  made  by  selecting  three  dry  block  which  will  pass 
visual  inspection  (§  318)  and  weighing  them  separately  on 
the  large  spring  balance  (§37  la).  They  should  then  be 
immersed  in  water  for  7  days,  at  the  end  of  which  time  they 
are  removed,  carefully  surface  dried  and  again  weighed. 


342        Testing  and  Sampling  Equipment 

The  difference  in  weights,  before  and  after  immersion,  is 
calculated  for  each  block  as  per  cent  of  water  absorbed  on 
the  basis  of  the  dry  weight.  An  average  of  the  three  tests 
should  be  reported  as  the  final  result. 

383.  Specific  Gravity,     (a)  Ordinarily  the  specific  gravity 
of  bituminous  materials,  such  as  oils,  asphalts,  and  refined 
tars,  should  be  determined  by  the  laboratory  but  at  times 
the  Inspector  may  wish  to  know  the  approximate  specific 
gravity  of  a  material,  when  a  laboratory  report  is  not  avail- 
able.   In  such  case  it  is  well  to  work  with  as  large  a  sample 
as  possible  and  to  have  the  temperature  of  the  material 
approximately  25°  C.   (77°  F.).     For  this  purpose  an  ordi- 
nary conical  top  one  gallon  oil  can  may  be  used.    The  clean 
dry  can  is  first  weighed  empty  on  the  large  spring  balance 
(§  37 la)  and  the  pointer  set  at  zero.     It  is  then  completely 
filled  with  water  and  the  weight  of  the  water  recorded.    It 
is  next  emptied  and  when  dry  is  completely  filled  with  bitu- 
minous material.    In  the  case  of  a  semi-solid  product  it  will 
first  be  necessary  to  render  it  fluid,  by  the  application  of 
heat.    Upon  cooling  the  material  will  shrink  and  additional 
material  must  then  be  poured  in  until,  when  cool,  the  can 
is  completely  filled.    The  weight  of  the  contents  of  the  can 
is  then  ascertained  and  this  weight  divided  by  the  weight  of 
water   originally   obtained   gives   the   approximate   specific 
gravity  of  the  material. 

(6)  In  the  case  of  bituminous  materials  which  are  suffi- 
ciently solid  to  be  handled,  a  ball  or  fragment  weighing 
approximately  100  grams  may  be  weighed  in  air  and  in 
water  and  its  specific  gravity  ascertained  exactly  as  de- 
scribed for  non-bituminous  materials  (§  376a).  The  specific 
gravity  of  an  asphalt  block  or  of  not  less  than  a  10-pound 
sample  of  compressed  bituminous  aggregate  or  pavement 
sample  may  be  determined  in  the  same  manner  with  the 
large  spring  balance  (§  37 la). 

384.  Voids  in  Compressed  Bituminous  Paving  Mixtures. 
The  per  cent  of  voids  in  compressed  bituminous  paving  mix- 


Miscellaneous  Equipment  343 

tures  may  be  calculated  if  the  specific  gravity  and  per  cent 
by  weight  of  each  constituent  are  known,  as  well  as  the 
specific  gravity  of  the  compressed  mixture.  This  first  in- 
volves a  calculation  of  the  maximum  possible  density  which 
is  given  by  the  following  formula  in  which  D  represents 
the  maximum  possible  density,  W,  W1,  W2,  etc.,  represent 
the  weight  per  cents  of  the  various  constituents,  and  G,  G1, 
G2,  etc.,  their  respective  specific  gravities. 

D 1QQ          . 

'  W_      W^      W* 

G  +  G1  +  G2 

Thus,  for  example,  if  a  bituminous  aggregate  is  composed  of 
94  per  cent  of  broken  stone  with  a  specific  gravity  of  2.7 
and  6  per  cent  of  asphalt  with  a  specific  gravity  of  1.04  the 
maximum  possible  density  of  the  mix  is 
100 


94         6 


=  2.46. 


2.7  '   1.04 

If  the  actual  density  of  the  compressed  mix  as  found  is 
called  d  then  the  per  cent  of  voids  in  the  mix  is  ascertained 
by  the  following  formula: 

~  xr  . ,        100(0  -  d) 
%  Voids  =  -   -^p— 

Thus,  if  in  the  example  above  given  the  actual  density  of 

the  mix  is  found  to  be  2.30,  the  per  cent  of  voids  would  be 

100(2.46  -  2.30) 


2.46 


=  6.5%. 


MISCELLANEOUS  EQUIPMENT 

385.  Sampling.  No  special  sampling  devices  are  ordi- 
narily needed  by  the  Inspector  although  when  required  to 
sample  large  quantities  of  material  at  one  time,  such  as 
sand  or  cement,  tube  samplers  will  be  found  convenient. 
Special  forms  of  thief  samplers  may  also  prove  useful  for 
sampling  bituminous  materials  in  large  tanks.  Whatever 


344        Testing  and  Sampling  Equipment 

device  or  method  may  be  used  for  sampling,  the  Inspector 
should  always  remember  that  no  matter  how  carefully  and 
accurately  tests  are  conducted,  test  results  can  be  no  more 
representative  than  the  samples  themselves.  It  is,  there- 
fore, most  important  that  the  relatively  small  quantity  of 
material  in  the  sample  be  so  selected  that  it  is  actually 
representative  of  the  larger  bulk  of  material  sampled. 
Great  care  should  be  taken  that  samples  are  not  contami- 
nated with  dirt  or  other  extraneous  matter  and  that  the 
sample  containers  are  perfectly  clean  and  dry  before  filling. 
Immediately  after  filling,  the  sample  containers  should  be 
closed  and  properly  marked  (§  389)  for  identification. 
Samples  should  be  packed  for  shipment  in  such  manner 
that,  during  transit,  leakage  of  contents,  breakage,  or  con- 
tamination by  packing  material,  is  entirely  prevented  as 
well  as  obliteration  or  removal  of  identification  marks. 

386.  Thermometers.  While  the  ordinary  unprotected 
laboratory  thermometer  is  best  suited  for  use  in  connection 
with  the  plant  inspection  tests  here  described,  it  is  unsuit- 
able for  obtaining  records  of  the  temperature  of  material 
as  prepared  for  use  in  certain  bituminous  types  of  construc- 
tion. Large  stationary  kettle  thermometers  should  pref- 
erably be  supplied,  by  the  contractor,  for  recording  the 
temperature  of  all  bituminous  materials  heated  in  kettles 
or  tanks.  For  ascertaining  the  temperature  of  heated  aggre- 
gates and  bituminous  mixes,  the  Inspector  should  be  pro- 
vided with  an  armored  thermometer  with  a  temperature 
range  suited  to  the  particular  requirements  of  the  job. 
For  ordinary  paving  plant  and  street  inspection,  a  ten-inch 
armored  thermometer  with  scale  graduated  from  200°  to 
650°  F.  in  5°  divisions  is  very  serviceable.  Such  a  ther- 
mometer is  manufactured  particularly  for  asphalt  testing,1 
and  may  be  plunged  into  a  heated  bituminous  aggregate  to 
a  depth  of  4|  inches.  The  lower  part  of  the  stem  is  com- 

1  Taylor  Instrument  Co.,  Rochester,  N.  Y.,  Cat.  No.  1107,  Asphalt 
Testing  Thermometer. 


Miscellaneous  Equipment  345 

pletely  protected  by  a  metal  casing  and  the  bulb  is  immersed 
in  a  mercury  packing.  The  upper  part  of  the  stem  is  also 
protected  by  the  metal  casing,  except  for  the  reading  face. 
After  use  and  while  still  warm,  the  thermometer  should  be 
wiped  with  a  clean  cloth  and  any  adhering  bitumen  should 
be  removed  with  kerosene. 

387.  Measurement  and  Visual  Inspection.     The  Inspec- 
tor should  ordinarily  be  provided  with  a  50-foot  steel  tape 
graduated  on  one  side  in  feet  and  inches  and  on  the  other 
in  feet  and  tenths  of  a  foot.    A  single  hinge  foot  rule  gradu- 
ated in  a  similar  manner  will  be  useful.    In  the  case  of  brick 
or  block  inspection,  a  small  wooden  gauge  with  the  three 
specified  dimensional  limits  marked  or  notched  thereon  will 
also  be  useful.    Such  a  gauge  may  be  made  in  a  few  minutes' 
time  by  the  Inspector  on  the  job.    A  small  pocket  magnify- 
ing glass  may  in  some  cases  prove  a  valuable  part  of  the 
Inspector's  equipment.     In  addition  a  string  level,  a  short 
plumb  line  and  a  short  stout  screw  driver  will  at  times 
prove  most  handy  accessories  for  the  purpose  of  measurement. 

388.  Selection  of  Equipment.     It  is  quite  essential  that 
the  Inspector's  equipment  be  as  light  and  compact  as  possi- 
ble and  practically  all  of  the  testing  apparatus  listed  above 
has  been  selected  from  this  standpoint.    Together  with  addi- 
tional equipment  listed  under  the  various  types  of  pave- 
ment, practically  everything  that  the  Inspector  may  need 
for  a  single  job,  with  the  exception  of  sample  containers 
in  quantity,  may  be  packed  in  an  ordinary  suitcase  and  in 
most   instances   considerably  less  space  than  this  will  be 
required.    This  statement  does  not,  of  course,  include  such 
articles  as  templates,  spades,  shovels,  etc.,  which  if  needed 
may  be  made  or  borrowed  on  the  job.    Just  what  will  be 
needed,  for  a  given  piece  of  work,  will  depend  largely  upon 
specification  requirements  and  the  accessibility  of  the  test- 
ing laboratory.     Judicious  selection  made  upon  this  basis 
will  keep  the  Inspector's  equipment  to  the  minimum  of 
weight  and  bulk. 


CHAPTER  XVIII 

RECORDS  AND  REPORTS 
SAMPLES 

389.  Identification.     Each  sample  of  material  submitted 
to  the  laboratory  should  be  plainly  identified  by  a  mark  or 
number  which  should  never  be  duplicated  for  any  other 
sample  in  connection  with  the  same  job.    In  many  instances 
it  is  impossible  to  place  such  a  mark  directly  on  the  material 
and  it  is  then  necessary  to  mark  the  container  or  to  securely 
attach  to  the  container  an   identification  tag   bearing  the 
mark.    The  outside  wrapping  of  a  sample,  shipped  by  mail 
or  express,  should  never  be  depended  upon  to  carry  the 
identification  mark  as  the  wrapping  is  likely  to  be  lost  or 
destroyed  before  the  mark  is  recorded  by  the  laboratory. 
Care  should  be  taken  that  identification  marks  are  per- 
fectly legible  and  that  during  transit  they  will  not  be  obliter- 
ated or  defaced.    The  Inspector  should  record,  in  his  diary, 
for  future  reference  the  marking  of  each  sample  submitted 
together  with  the  general  information  forwarded  the  labo- 
ratory in  connection  with  the  sample. 

390.  General  Information.    A  notice  of  the  shipment  of 
each  sample  should  be  promptly  mailed  to  the  laboratory 
together  with  such  information  as  should  be  made  a  matter 
of  record  or  which  will  assist  the  laboratory  in  determining 
what   interpretation   should   be   placed   upon   test   results. 
Such  information  may  include  any  .or  all  of  the  following 
items : 

Identification  mark. 

Name  or  type  of  material  including  trade  name,  if  any. 

346 


Samples  347 

Name  and  address  of  producer,  consignor,  or  owner  of 
the  deposit  in  case  of  natural  products. 

Location  of  plant  or  deposit  from  which  material  is  shipped 
or  secured. 

Purpose  for -which  sample  is  to  be  tested,  such  as  suita- 
bility for  a  given  use,  or  conformity  with  a  given  speci- 
fication which  should  be  clearly  indicated. 

Name  and  location  of  road  or  street  on  which  the  material 
is  proposed  for  use  or  has  been  used.  (In  the  latter  case 
the  exact  location  of  use  should  be  noted.) 

Place  and  date  of  taking  sample. 

Quantity  of  material  represented  by  sample. 

Place  from  which  sample  was  taken,  such  as  quarry, 
crusher,  bin,  pit,  plant,  car,  wagon,  barge,  storage  pile, 
mixer,  tank,  barrels,  drums,  distributor,  or  pavement. 

In  case  of  shipment  by  freight,  date  of  such  shipment  or 
date  of  receipt  at  destination,  together  with  car  number. 

Date  material  used,  or  to  be  used  if  satisfactory. 

General  comments  and  queries,  including  any  observa- 
tion that  the  Inspector  cares  to  make  relative  to  his 
own  suspicions  or  tests,  and  any  question  regarding 
the  sample  which  he  wishes  to  have  specifically  answered 
by  the  laboratory. 

In  well-organized  work  printed  forms  are  frequently  used 
in  connection  with  the  submission  of  samples.  Such  forms 
contain  headings,  similar  to  those  above  listed,  under  which 
the  Inspector  is  expected  to  enter  the  desired  information. 
It  is  advisable  for  the  Inspector  to  retain  a  carbon  copy  of 
all  information  which  he  furnishes  the  laboratory. 

391.  Location  Where  Used.  Whenever  material  which 
has  been  sampled  for  laboratory  or  field  tests  is  used  on 
a  job  the  Inspector  should  enter,  in  his  diary,  the  exact  loca- 
tion on  the  road  where  the  material  is  used  together  with 
the  identification  mark  and  name  of  the  sample.  Such  a 
record  will  be  of  great  service  in  the  later  correlation  of 


348  Records  and  Reports 

service  results  with  the  characteristics  of  the  material,  as 
determined  by  test.  Station  numbers  may  be  used  to 
locate  positions  on  the  road  but,  in  addition  to  this,  it  is 
well  to  also  note  distinguishing  landmarks  or  roadside 
features,  such  as  the  number  or  name  of  a  building,  the 
intersection  of  another  highway,  the  name  of  the  owner  of 
adjacent  property,  the  distance  from  the  upper  or  lower 
end  of  a  grade,  the  distance  from  a  gate  post  or  fence  corner, 
or  from  some  particularly  prominent  tree,  etc. 

392.  Test  Reports.  The  Inspector  should  retain  copies 
of  all  test  reports  furnished  him  by  the  laboratory  and 
should  enter  in  his  diary  the  results  of  all  field  tests  which 
he  himself  makes.  He  should  also  include  the  results  of 
field  tests  in  reports  which  he  may  make  to  the  Engineer 
from  time  to  time. 


PROGRESS  OF  WORK 

393.  Daily  Records.     A  daily  record  of  progress  of  work 
should  be  kept  by  the  Inspector  and  a  daily  report  of  such 
progress  should  be  forwarded  the  Engineer.     Special  report 
forms  are  often  used  for  this  purpose  in  which  the  work 
done  during  the  day  is  shown  by  station  distances  for  the 
various  items  of  work  such  as  rough  grading,  fine  grading 
construction  of  foundation,  construction  of  wearing  course, 
trimming    shoulders,    construction    of    curb,    gutters,    etc., 
according  to  the  class  of  work  involved.     Upon  receipt  of 
such  report  by  the  Engineer  the  record  is  taken  off  upon  a 
large  chart  showing  the  entire  length  of  the  road  or  pave- 
ment divided  into  stations.     The  Engineer  thus  has  con- 
stantly at  hand  a  diagram  showing  the  status  of  the  work 
at  a  glance. 

394.  Weekly  Summaries.    Weekly  summaries  of  progress 
of  work  are  in  general  similar  to  the  daily  records  but  may 
be  more  complete  in  certain  details  which  are  recorded  in 
the   Inspector's  diary.     Thus  quantities   of  materials  re- 


Progress  of  Work 


349 


ceived  on  the  job,  quantities  of  materials  used  and,  in  cer- 
tain cases,  items  of  work  not  shown  on  the  daily  reports  are 
recorded,  together  with  a  statement  of  the  number  and 
kind  of  samples  submitted  to  the  laboratory,  a  tabulation 
of  field  tests  made  by  the  Inspector  and,  in  some  cases,  cost 
data  relative  to  labor  and  materials. 

395.  Paving  Plant  Operation.  The  plant  Inspector 
should  forward  the  Engineer  daily  reports  of  plant  opera- 
tion showing  the  results  of  tests  made  on  the  various  materi- 
als, temperature  records,  actual  weights  and  proportions  of 
the  constituents  used  in  each  type  of  mix,  total  quantity  of 
each  mix  produced  and  sent  out  by  the  plant,  and  the 
number  of  square  yards  laid  with  each  type  of  mix.  No 
single  report  form  is  well  suited  for  all  kinds  of  paving  work, 
unless  it  contains  items  which  may  not  apply  to  the  par- 
ticular class  of  pavement  under  inspection.  The  proper 
form  is,  therefore,  usually  prepared  by  the  Engineer  to 
meet  his  own  requirements.  The  following  form  in  con- 
nection with  sheet  asphalt  work  will,  however,  serve  as  an 
example  of  what  may  be  required  of  the  plant  Inspector  in 
the  way  of  daily  reports. 


DAILY  REPORT  OF  PLANT  INSPECTOR  FOR  SHEET 
ASPHALT  PAVEMENT 

Location  of  work Date 

Binder  Mix,  No.  boxes No.  loads Sq.  yds.  laid 

Surface  Mix,    "        "     "        " "      "      "  

ASPHALT  CEMENT  USED 


Material 

Kind 

Lab.  No. 

Proportions 

Penetration  A.  C. 

Binder 

Surface 

Asphalt 
Flux 

100  Ibs. 

100  Ibs. 

Binder 
Surface 

350 


Records  and  Reports 


BINDER  Mix 


Material 

Box  Weight 

Per  cent 

Box  Weight 

Per  cent 

Stone 

Sand 

A.  C. 

SURFACE  Mix. 


Material 

Box  Weight 

Per  cent 

Box  Weight 

Per  cent 

Sand 

Filler 

rtoqo-i  VIJJ 

A.  C. 

BINDER  AGGREGATE 


Size,  Per  cent 

Stone 

Sand 

Mix 

1  inch-1^  inches 
|  inch-10  mesh 
Passing  10  mesh 

Quantities  of  Material 


351 


HOT  SAND 


Time 

Size 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

10-20 

20-30 

30-40 

40-50 

50-80 

80-100 

100-200 

Passing  200 

TEMPERATURES 


Time 

A.  C. 

Stone 

Binder  Mix 

Sand 

Surface  Mix 

Samples  submitted  to  Lab.  Stone Sand Filler. 

R.  A Flux..          ..A.  C. 


Signature 


QUANTITIES  OF  MATERIAL 


396.  Material  Received.  The  Inspector  should  keep  in 
his  diary  a  record  of  quantities  of  various  materials  received 
on  the  job  and,  in  case  of  distribution  along  the  sides  of  the 
road,  he  should  note  the  spacing  of  individual  lots  as  a 
check  upon  estimates  of  quantities  needed  to  complete  the 
work  in  accordance  with  specification  requirements.  Such 
records  should  be  included  in  his  daily  or  weekly  reports 
together  with  a  statement  of  samples  taken  and  tested  or 
submitted  to  the  laboratory. 


352  Records  and  Reports 

397.  Material  Used.     No  material,  requiring  laboratory 
test,  should  be  allowed  to  be  used  until  accepted  upon  the' 
basis  of  test  results,  unless  its  use  without  previous  testing 
is  specifically  authorized  by  the  Engineer.     The  Inspector 
should  see  that  all  rejected  material  is  promptly  removed 
from  the  site  of  work  and  that  it  is  not  later  used  on  any 
part  of  the  job.    Deductions  for  such  rejections  and  removals 
should  be  made  from  the  record  of  material  received  in 
working  up  his  weekly  summaries.     A  daily  record  should 
be  kept  of  quantities  of  materials  actually  used  together 
with  the  yardage  or  volume  of  each  class  of  work  performed. 
The  use  of  materials  which,  upon  the  basis  of  field  tests, 
fail  to  pass  the  specification  requirements  should  be  allowed 
only  at  the  risk  of  the  Contractor  with  the  warning  that 
the  work  in  which  it  is  so  used  may  be  rejected  at  the  dis- 
cretion of  the  Engineer,  who  will  decide  upon  the  impor- 
tance of  the  variations  from  specification  requirements.     The 
use  of  any  material  should  not,  however,  be  stopped  upon 
the  basis  of  field  test  results  obtained  from  a  single  sample. 
Material  variation  from  specification  requirements  should 
always  be  checked  by  tests  made  upon  one  or  more  addi- 
tional samples.     The  daily  record,  of  each  material  used, 
may  be  entered  upon  the  daily  report  of  progress  of  work 
and  should,  for  each  material,  show  the  number  or  identi- 
fication mark  of  the  sample  or  samples  which  represent  the 
particular  lot  of  material. 

398.  Checks  on  Quantities.     The  Inspector  should  check 
quantities  of  materials  shown  on  bills  of  lading,  etc.,  by  his 
own  measurements  of  weight  or  volume,  a  record  of  which 
should  be  kept  in  his  diary.     The  various  diagrams  given 
under  the  different  types  of  work  may  be  of  assistance  to 
him  in  such  determinations,  but  as  they  will  not  exactly 
fit  all  cases  it  will  frequently  be  advisable  for  him  to  carry 
in  his  diary  small  charts  or  diagrams  which  he  may  pre- 
pare to  meet  the  conditions  of  the  particular  job  under 
inspection. 


Cost  Data  353 

COST  DATA 

399.  Labor.    When  work  is  done  upon  a  force  account 
basis  it  is  necessary  to  keep  a  record  of.  the  force  employed 
and  to  report  daily  the  number  of  hours  work  of  each  em- 
ployee.    When  a  large  force  is  employed,  and  the  force  is 
scattered  over  a  considerable  length  of  highway,  the  serv- 
ices of  a  timekeeper  will  be  needed  for  this  purpose,  but 
on  small  jobs  where  the.  force  is  concentrated  the  Inspector 
is  sometimes  required  to  subm.it  a  daily  report  showing  the 
number  of  each  class  of  labor,  the  hours  of  work  performed, 
the  rate  of  compensation  and  the  amount  of  money  in- 
volved.    For  this  purpose  he  should  be  provided  with  a 
special  report  form.    In  addition  to  this  he  may  be  required 
to  show  the  distribution  of  cost  among  various  items  of  the 
work,  such  as  spreading  stone,  distributing  bituminous  ma- 
terial, laying  brick,  etc. 

400.  Materials.     On  certain  jobs  it  may  be  necessary  to 
keep  a  record  of  the  cost  of  materials  used.    As  the  quanti- 
ties of  materials  used  should  always  be  recorded  by  the 
Inspector  under  the  various  items  of  work,  the  distribution 
of   costs  is   a  simple  matter   provided   measurements   are 
made  upon  the  proper  unit  basis  and  the  unit  price  is  known. 


GENERAL  RECORDS 

401.  The  Inspector's  Diary.  The  Inspector's  diary  should 
be  his  constant  companion  and  in  it  he  should  keep  a  com- 
plete daily  record  of  all  matters  pertaining  to  his  work, 
especially  such  data  as  will  be  included  in  his  reports  to 
the  Engineer.  The  entries  should  be  neat  and  legible  and 
all  calculations  of  quantities  and  costs  should  be  clearly 
shown,  together  with  details  and  calculations  in  connection 
with  all  field  tests  which  he  may  make.  By  so  doing,  possi- 
ble errors  may  be  most  readily  located  and  corrected.  The 
diary  should  be  of  pocket  size.  If  of  the  loose  leaf  type  the 


354  Records  and  Reports 

pages  should  be  numbered  consecutively  so  that  once  re- 
moved from  the  cover  they  may  be  reassembled  in  proper 
sequence. 

402.  Deviation     from     Specifications.     The     Inspector 
should  always  carry  with  him,  for  reference,  a  copy  of  the 
specifications.    All  deviation  from  the  specification  require- 
ments should  be  noted  in  his  diary,  together  with  notation 
of  his  action  in  connection  with  same,  such  as  acceptance 
of  material  or  work  with  warning  to  the  contractor,  rejec- 
tion of  material,  etc. 

403.  Special  Instructions  from  the  Engineer.    All  special 
instructions  from  the  engineer  not  received  in  writing  should 
be  dated  and  entered  in  the  Inspector's  diary  as  a  record  of 
what  he  is  expected  to  do  under  the  conditions  covered  by 
such  instructions.    This  is  particularly  advisable  in  case  the 
Engineer  sees  fit  to  fix  certain  allowable  limits,  within  the 
specification  requirements,  or  agrees  with  the  Contractor 
to  allow  certain  deviations  from  the  specifications,  or  places 
a  definite  interpretation  upon  some  requirement  which  may 
appear  to  be  indefinite.     Upon  the  first  opportunity  the 
Inspector  should  request  the  Engineer  to  O.K.  such  instruc- 
tions as  entered  in  his  diary. 

404.  Report  Forms.     Report  forms  should  be  so  devised 
as  to  show  clearly  and  concisely  all  of  the  information  re- 
quired by  the  Engineer.     It  is  impracticable  to  utilize  a 
single  form  for  all  classes  and  conditions  of  work  but  the- 
general  arrangement  and  subject  matter  is  illustrated  in 
the  following  daily  report  form,  adapted  for  use  in  connec- 
tion with  the  construction,  by  contract,  of  a  bituminous 
macadam  pavement  upon  an  old  reshaped  macadam  road, 
which  is  made  to  serve  as  foundation. 


General  Records 


355 


INSPECTOR'S  DAILY  REPORT  ON  BITUMINOUS 
MACADAM 


Location  of  work Date 

Weather Temperature. 

PROGRESS  OF  WORK 


From 
Station 

To 
Station 

Remarks 

Reshaping  old  road  

Placing  broken  stone  
1st  application  bit.  mat.  . 
Seal  coat  
Trimming  shoulders  

MATERIALS 


Material 

Used 

Received 

Sample 
No. 

Total 

Sq.  yd. 

Quantity 

Sample 
No. 

New  stone  in  foundation  .... 
Coarse  stone  wearing  course  . 
Chips  
Bit.  mat.,  1st  application.  .  .  . 
Bit  mat    seal  coat  

1 

TESTING  AND  SAMPLII  a 
Tests  of  Broken  Stone 


Grade                   

Samnlp  No 

«                                    "            " 

«                                    "            " 

356 


Records  and  Reports 

Submitted  to  Laboratory 


Material 

Sample  No. 

f  10  i!OtJ(;-jt:J 

AKt.>  //    •-(<» 

. 

Temperature  of  Bituminous 
Material 


Time 

Temperature 

Remarks: 


•KfF 


Signature 


a 


• 


CHAPTER  XIX 
TYPICAL  MATERIAL  REQUIREMENTS 

Unless  otherwise  indicated  by  footnotes,  all  of  the  follow- 
ing specification  requirements  are  tabulated  from  typical 
specifications  of  the  U.  S.  Bureau  of  Public  Roads.1  They 
serve  to  illustrate  common  physical  and  chemical  char- 
acteristics determined  by  test  which  are  commonly  included 
in  specifications  for  various  types  of  materials.  When  a 
test  value  is  followed  by  a  +  sign,  the  sign  should  be  inter- 
preted as  meaning  not  less  than  the  value  given.  When 
a  test  value  is  followed  by  a  -  sign,  the  sign  should  be  in- 
terpreted as  meaning  not  more  than  the  value  given. 


NON-BITUMINOUS  MATERIALS 


405.  Broken  Stone. 


Type  of  Road 

Total  Per  Cent  Passing  Screens 

•g^- 

j§ 

ff 

3" 

2*" 

2* 

U" 

|« 

I* 

4 

WATERBOUND                

95+ 

25-75 

15- 

95+ 

25-75 

15- 

95+ 

40-80 

7+ 

1  

Top  course      

BITUMINOUS  SURFACE  

95+ 

85+ 

15- 
15- 

BITUMINOUS  MACADAM.  .  .  . 

95+ 

25-75 

15- 
95+ 

25-75 

95+ 

15- 

7+ 

8 

Chips 

BITUMINOUS  CONCRETE  
(One-size  stone) 

95+ 

15- 

15- 

8 

Chips  for  seal  coat  

U.  S.  Dep't.  Agriculture  Bulletins  691  and  704. 
357 


358          Typical  Material  Requirements 
405.   Broken  Stone  —  Continued. 


Type  of  Road 

Total  Per  Cent  Passing  Screens 

l"i 

J. 

M  M 

Hfl 

3" 

2i" 

2* 

4 

BITUMINOUS  CONCKBTE  — 
(Coarse  graded) 
Coarse  aggregate  l  
Chips  for  seal  coat  

95+ 

25-75 

95+ 
95+ 

15- 
15- 

8 

8 

BITUMINOUS  CONCRETE.  .  .  . 
(Topeka  type) 
Stone  aggregate  z  

80- 

SHEET  ASPHALT  BINDER.  .  . 
Stone  aggregate  *".  

95+ 

8 

CEMENT  CONCRETE  BASE.  . 

95  + 

' 

40-75 

15- 

8 

CEMENT  CONCRETE  PAVE.  . 

95+ 

40-75 

15- 

8 

1  For  fine  aggregate  see  §  407.  2  For  sand  aggregate  see 

406.  Gravel. 


§407. 


Type  of  Road 

Total  Per  Cent  Passing  Screens 

j3 

M5g 

•S  S 

I1 

3" 

2" 

t* 

1* 

P 

r 

1" 

WATERBOUND  
Bottom  Course 

95+ 

95+ 

25-75 

25-75 

85  + 

25-50 
25-50 

rjoafl 
15-35 

15-35 

50+ 
50+ 

Coarse  ag  ret.  on  J"  .-• 

Top  (or  both)  courses  
Entire  aggregate  .  .    ;  .  i  r-.i.—.— 

Coarse  ag.  ret.  on  J"  
Pine  ag.  passing  J*  

BITUMINOUS  SURFACE  
Pea  gravel                    

15- 

BITUMINOUS  CONCRETE  

95+ 

25-75 

95  + 

15- 
15- 

(Coarse  graded) 

Gravel  for  seal  coat  

CEMENT  CONCRETE  BASE  

95+ 

40-75 

15- 

Coarse  aggregate3  

For  fine  aggregate  see  §  407. 


Bituminous  Materials 


359 


407.   Sand. 


c 

Pe 

r  Cent 

Passin 

gMe 

shSi 

3ve 

£'§ 
=  tl 

4 

^ 

10 

20 

40 

50 

100 

200 

Ij 

sa 

II 

BITUMINOUS  CONCRETE 
(Coarse  graded) 

100 

30-70 

10- 

BITUMINOUS  CONCRETE 
(Topeka  type) 
Sand  aggregate  2  

100 

10- 

SHEET  ASPHALT  BINDER  3 
Sand  aggregate  2  

100 

CEMENT  CONCRETE  BASE 

100 

"  20+ 

50— 

10— 

B-i 

75+ 

CEMENT  CONCRETE  PAVEMENT 

100 

50-80 

20- 

5— 

i- 

100+ 

BRICK  OR  BLOCK 
Sand  cushion    

100 

5  — 

100 

75+ 

Grouting  sand  4  

100 

80+ 

5- 

75+ 

1  For  coarse  aggregate  see  §§  105  and  106.  2  For  stone  aggregate  see  §  105. 

8  For  sand  grading  for  surface  mixture  see  §  279. 

« A.  S.  T.  M.  Tentative  Specifications  recommended  by  Com.  D-4  in  1919. 

BITUMINOUS  MATERIALS 
408.   Oil  and  Asphalt  Products  for  Surface  Treatment. 


Material 

Heavy 
Distillate 

Heavy  Crude 
or  Cut-back 

Cut-back 
Asphalt» 

Residual 

Dust 

Cold  Surface 

Cold  Surface 

Hot  Surface 

Use 

Palliative 

Treatment 

Treatment 

Treatment 

Specific  gravity  25°  C  
Flash  point,  open  cup  
Specific  visocity,  25°  C  

0.940  - 
100°  C.  + 
10- 

0.935-0.970 
50°  C.  - 
80-120 

0.890  + 
25-35 

0.980  + 
80°C.+ 

"                        100°  C  

Float  test  32°  C...  
Loss  163°  C.,  5  hours  
Float  50°  C.  on  residue.    .    . 

15%- 
Liquid 

30%- 
90  sec.  + 

30-40% 

60  sec.  + 
15%- 
110  sec.  + 

Penetration  25^  C.of  residue  . 
Solubility  in  carbon  disulphide  . 
Insol.  in  86°  B.  naphtha  
Sp.  gr.  distillate  to  200°  C  

99.8%  + 

99.5%  + 
6.0%  + 

50-85 
99.5%  + 

0.73-0.78 

99.5%  + 
6.0%  + 

1  Am.  Soc.  for  Municipal  Improvements,  1919. 


360          Typical  Material  Requirements 

409.  Tar   Products   for  Surface    Treatment    and    Cold 
Patching. 


Material 

Light 
Refined  l 

Refined  or 
Residual 

Cut  Back 

Use 

Cold  Surface 
Treatment 

Hot  Surface 
Treatment 

Cold 
Patching 

Specific  gravity  25°  C 

1.100-1.180 
10-352 

5%- 
30%- 
40%- 
90%  + 

1.130- 
60-150 

15%- 

25%  - 
85%  + 

1.100-1.200 
40-70 

2%- 
15-25% 
30%- 
80%  + 

"        viscosity  40°  C  

Float  test  32°  C. 

Total  distillate  to  170°  C...  . 

"270°C  
"  300°  C. 

Solubility  in  carbon  disulphide..  .... 

1  Am.  Soc.  for  Municipal  Improvements,  1918. 

2  A  range  of  5  allowed  for  any  one  job,  exact  limits  to  be  controlled  by  climatic 
conditions  and  type  of  road  treated. 


410.   Asphalt  Emulsion  for  Cold  Patching. 


Total  distillate  to  260°  C 

Oil  distillate  to  260°  C 

Tests  on  residue  from  distillation  to  260°  C. 

Specific  gravity  25°  C  ...........  . 

Penetration  at  25°  C 

Solubility  in  carbon  disulphide 

Insoluble  in  76°  B.  naphtha 

Fixed  carbon  ......  —  .  .  ....  .  ,.,n)j  ;  h,i««m 

Ash  ...................  »t'»7€'£  9%.'>iw  to*wi' 

Paraffin  scale  .....  .\.  ^  b«.k»  «i«(«i«-s' 

Ductility  at  25°  C  ...... 


32%- 


1.01+ 
150-250 

98.5%+ 

8-28% 

6-15% 

1%- 
4.7%- 
40+ 


411.  Refined  Tars  for  Bituminous  Macadam  or  One- 
size  Stone  Bituminous  Concrete. 


Conditions 

1 

0^ 

«<N 

cfl  +j 

Float  Test 
at  50°  C. 
(seconds) 

Per  Cent  Total 
Distillate 

Melt.  Point 
Resid.  °  C. 
(Ring  and  Ball). 

Per  Cent 
Soluble  in  Car- 
bon Disulphide 

to 
170°  C. 

to 
270°  C. 

to 
300°   C. 

Northern  U.  S. 
Low  carbon  tar  

1.15-1.20 
1.20-1.25 

1.15-1.20 
1.20-1.25 

120-150 
150-180 

1- 
1- 

10- 
10- 

20- 

20- 

65+ 
65 

97+ 
80-97 

97+ 
80-97 

Medium  carbon  tar  .  .  . 
Southern  U.  S. 
Low  carbon  tar  
Medium  carbon  tar.  .  .  . 

1  New  York  State  Highway  Commission,  1919.  Material  must  flow 
readily  from  bung  of  barrel.  Must  not  separate  when  agitated  for  3 
minutes  with  clean  washed  and  drained  trap  rock  in  proportions  of  1£ 
oz.  emulsion  to  1  pound  of  small  broken  stone. 


Bituminous  Materials 


-UJ    OIUB8JQ 


I    I    I 

IN       <N       <N 

000 


ic         cucooic 


o:  »c  a-  ic  05  «3         05  ic 
050505050505         05O5 


'O  oSS  *« 
anpisajj 

jo  :°3<1 


:    OQ 

i     cttn 


89I  8807 
s-inojj  g 


I    I    I    I 


I  I 


So 
(N 

S!£ 


>      68 

)-     -     lCr-l 


PUB  3utH) 
'O  o 


CO  CO 


88 

*4 


!+S 

isi 


(dn0 


+       + 

«o:          to : 
i>  i> 


01       o"T   To>c'T< 

I-H  1C  CM  >O       O  (N  iC  1-1  ( 

OO  OO       <NOO<N< 


<! 

s 


il  3 


•  5     :  W 

:^^"2 


-  Is- 

n  .i  8  Pr 


U  :  m 


J«o 


"        .  ''         -•>1^'         •*»  M 


*ae 

3ll 


362          Typical  Material  Requirements 

413.  Tar  Pitch  for  Grout  for  Joint  Filler.1 

Specific  gravity  at  60°  F.  (15.5°  C.) 1.23-1.33 

Melting  point  (cube  method  in  water) 115-135°  F. 

Insoluble  in  hot  benzol  or  chloroform 20-35  % 

Inorganic  matter 0.5  %  - 

Ductility  at  77°  F.  (25°  G.) 60  c.  m.  + 


414.  Creosoting  Oil.5 


Coal  Tar 

Oil  Dis- 

Material 

tillate 
65%  + 
»Ref.  or 
Filtered 

Coal  Tar 
Distillate 

Water 
Gas 
Tar3 

Tar 

35%- 

Water                                        

3%  - 

3%  - 

3%  - 

Insoluble  in  benzol                 

3%  - 

0.5  %  - 

2%  - 

Specific  gravity  38°  C.             

1.07-1.14 

1.06  + 

1.11-1.14 

Total  water  free  distillates 

To  210°  C.           

5%  - 

5%  - 

5%  - 

"  235°  C 

25%  - 

15%  _ 

15%  _ 

"   315°  C 

40%  - 

"   355°  C  

25%  + 

Sp.  gr.  distillate  235°-315°  C.  at  38°  C. 
"     "          "        315°-355°C.  "       " 

1.03  + 
1.09  + 

1.03  + 
1.09  + 

"     "  total   distillate   to   355°  C.    at 

38°  C                                            

0.99-1.03 

Float  test  at-  70°  C.  on  residue  if  35  %  + 

80  sec.  - 

«          «       «          tt        «          «         "1Q%  + 

50  sec.  - 

Coke  residue  

10%  - 

2% 

1  Am.'  Soc.  for  Municipal  Improvements,  1918. 

2  Amer.  Soc.  for  Testing  Materials  1918,  Tentative, 
a  Presented  to  Society  for  information. 


INDEX 


Abrasion  test 
for  gravel,  41 
for  rock,  22 
for  sand,  41 
values  for  rock,  20 
Absorption  test,  25,  341 
Amphibolite,  13 
Andesite,  13,  14 
Asphalt  (see      also      Bituminous 

Materials) 
cement,  64 
classification,  65 
coefficient  of  expansion,  80 
contents,  test  for,  97 
cut-back,  66 
emulsions,  66 
fillers,  66 
for  binder  course,  236 

bituminous     earth     pave- 
ment, 245 

bituminous  macadam,  157 
coarse    graded  bituminous 

concrete,  227 
one  size  stone  bituminous 

concrete,  221 
sheet  asphalt,  240 
Topeka  pavement,  231 
native,  64,  65 
petroleum,  63,  64 
rock,  67 
sampling,  80 
specifications  for  construction, 

361 
tests,  88 


volume  of,  75,  77 

weight  of,  73 
Asphalt  block,  270 

inspection,  272 

sampling,  272 

tests,  271 
Asphalt  block  pavements,  250,  270 

compaction,  255 

cushions  for,  252 

foundations  for,  251 

inspector's  equipment,  281 

joint  filling,  256 

laying,  254 

maintenance,  280 
Asphalt  cement  (see  Asphalt) 
Asphaltenes,  determination  of,  99 
Asphaltic    concrete    (see  Bitumi- 
nous Concrete) 

Asphalt    macadam    (see    Bitumi- 
nous Macadam) 
Augite,  17 

B 

Basalt,  13,  14 
Binder  course,  236 
Bitumen 

definition,  58 

determination  of,  98 

volume  of,  75 

weight  of,  74 
Bituminous  aggregates 

characteristics    of    aggregates, 

196 
of    bituminous    materials, 

197 
of  mix,  208 


363 


364 


Index 


Bituminous  aggregates 

combination     of      aggregates, 

205 

compacting,  217 
control  of  temperature,  201 
function  of  mineral  filler,  215 
heating  aggregates,  193,  214 
bituminous  material,  194 
inspector's  equipment,  210 
mixing,  195,  202 
proportioning,  195 
spreading,  216 
Bituminous    carpeting    mediums, 

144 

Bituminous  concrete  pavements 
(see  also  Bituminous  Ag- 
gregates) 

binder  course,  236 
coarse  graded  aggregate,  225 
bituminous  materials,   227 
coarse  aggregate,  225 
fine  aggregate,  226 
mix,  227 
seal  coat,  230 
foundations  for,  213 
inspector's  equipment,  248 
maintenance  of,  246 
measurement,    219,    222,    227, 

232 

method  of  construction,  213 
one  size  stone,  220 

bituminous  materials,   221 
mineral  aggregate  for,  220 
mix,  222 
seal  coat,  225 
Topeka  type,  230 

asphalt  cement,  231 
broken  stone,  230 
mix,  232 
sand,  231 
types,  212 

Bituminous  dips,  297 
Bituminous  dust  preventives,  143 


Bituminous  earth  pavements 
asphalt  cement,  245 
mineral  aggregate,  244 
mix,  246 

Bituminous  limestone,  244 
Bituminous  macadam,  151 

application  of  bituminous  ma- 
terial, 153 
asphalt  cement,  157 
broken  slag  requirements,  156 
broken  stone  requirements,  156 
definition,  151 
field  tests,  159 
filling  surface  voids,  155 
foundations  for,  152 
inspector's  equipment,  163 
maintenance,  162 
measurement,  159 
refined  tars  for,  158 
seal  coat,  155 

spreading  broken  stone,  152 
Bituminous    materials    (see    also 
Asphalt,  Petroleum  and 
Tar) 

classification,  58 
coefficient  of  expansion,  80 
composition,  58 
effect  of  water  in,  60 
fluxing,  194,  197 
laboratory  tests 

asphalt  contents,  97 

asphaltenes,  99 

burning  point,  95 

carbenes,  100 

coefficient  of  expansion,  91 

dimethyl  sulphate  test,  100 

distillation,  97 

ductility,  95 

fixed  carbon,  101 

flash  point,  95 

float  test,  93 

for  creosoting  oils,  102 

for  emulsions,   101 


Index 


365 


laboratory  tests 
melting  point,  94 
paraffin  scale,  101 
penetration  test,  93 
significance  of,  86 
specific  gravity,  88 
total  bitumen,  98 
viscosity,   91 
volatilization  test,  96 
water,  determination  of,  97 

manufacture,  59 

measurement,  71, 146, 159,  219, 
222,  227,  232,  238,  241 

sampling,  80 
containers,  81 

from  barrels  and  drums,  83 
from  loose  bulk,  84 
from  pipe  lines,  82 
from  tanks,  82 
general  precautions,  81 
prepared  joint  fillers,  85 
size  of  samples,  80 
time  and  place,  80 

storage,  61 

temperature  control  of,   59 

transportation,  61 

volume  of,  73,  77 

weight  of,  71 

Bituminous  paving  plant  inspec- 
tion (see  also  Paving 
Plant),  189 

Bituminous  sandstone,  243 
Bituminous    surface    treatments, 
138 

application,  140 

cover,  142 

definition,  138 

field  tests,  146 

inspector 's  equipment,  150 

maintenance,  149 

measurement,  146 

preparation  for,  139 

types  of,  138 


Brick 

paving,  259 
rattler  test,  261 
sampling,  265 
size,  262 

visual  inspection,  264 
Brick  masonry,  296 
Brick  pavements,  250,  259 
compaction,  255 
cushions,  252 
foundations  for,  251 
inspector's  equipment,  281 
joint  filling,  256 
joints,  262 
laying,  254 
maintenance,  280 
Broken  stone  (see  also  Rock) 
field  tests,  130 
for  binder  course,  237 

bituminous  macadam,  156 
coarse   graded    bituminous 

concrete,  225 
concrete  foundations,  174 
concrete  pavements,  174 
macadam,  129 
one  size  stone  bituminous 

concrete,  221 
surface  treatment,  145 
Topeka  pavement,  230 
manufacture  of,  14 

effect  on  size  and  grading, 

14 

measurement,  26,  131,  146, 
180,  219,  222,  227,  232, 
238. 

roads  (see  also  Macadam) 
definition,  121 
types,  121 
sampling,      29,      134,      161, 

183 

for  quality,  30 
for  size  or  grading,  31 
time  and  place,  29 


366 


Index 


tests 

size  or  grading,  24 

voids,  25 
voids  in,  27 
volume  of,  26,  29 
weight  of,  26,  28 
Burning  point  test,  95 


Calcite,  18 

Calcium  chloride,  298 
Carbenes,  determination  of,  100 
Car  tracks,  paving  adjacent  to, 

285 
Cementing   value,    determination 

of,  24,  42 

Cements    (see   also    Natural   Ce- 
ment  and   Portland   ce- 
ment) 
asphalt,  64 
hydraulic,  47 

classification,  47 
manufacture,  47 
properties,  48 
Cement-sand  beds,  252 
Chert,  13,  14,  19 
Clay 

classification,  33,  40 
occurrence,  32 
properties,  41 
tests 

cementing  value,  42 
elutriation,  42 
types,  40 

Coefficient  of  expansion  determi- 
nation, 91 
Cold  patching,  286 
Concrete 

composition,  165 
consistency,  171 
for  miscellaneous  structures, 

292 
forms,  293 


mixing,  170 

proportions,  165,  167 

water  for,  178 

waterproofing,  294 
Concrete  foundations  and  pave- 
ments, 165 

coarse       aggregate       require- 
ments, 174 

curing,   174 

details  of  construction,  167 

expansion  joints,  179 

field  tests,  179 

fine    aggregate    requirements, 
176 

finishing  surfaces,  173 

hydrated  lime  in,  178,  294 

inspector's    equipment,    186 

maintenance,   185 

measurement,  180 

placing  and  shaping,  171 

properties,   166 

reinforcement,  178,  294 

types  of  construction,   166 

water  for,  178 
Contours,  testing,  303 
Creosoting  oils,  71 

coefficient  of  expansion,  80 

specification  requirements,  362 

tests  for,  102 

volume  of,  73 
Crown  sections,  305 
Culverts 

clay  pipe,  287 

concrete  pipe,  288 

metal  pipe,  290 
Cushions    for    brick    and    block 

pavements,  252 
Cut-back  asphalts,  66 

D 

Diabase,  13,  14 

Dimethyl  sulphate  test,  100 

Diorite,  13,  14 


Index 


367 


Dips,   bituminous,  297 

Distillation  test,  97 

Dolomite,  13,  14,  18 

Ductility  test,  95 

Dust  preventives,  bituminous,  143 

E 

Eclogite,  13 
Elutriation  test,  42 
Emulsions,  66 

specification  requirements,  360 

tests  for,  101 
End  sections,  309,  312 
Expansion  joints,  179,  259,  283 

poured,  283 

prepared,  284 


Feldspars,  17 
Fillers 

asphalt,  66 

mineral,  215 

pitch,  71 
Fixed  carbon  determination,   101 
Flash  point  test,  95 
Flint,  13 

Float  test,  93,  336 
Fluxing,  194,  197 

G 

Gabbro,  13,  14 

Glutrin,  299 

Gneiss,  13,  14,  18,  21,  22 

Grading,  determination  of,  24,  43, 

324 

Granite,  13,  14,  18,  21,  22 
Granite  block   (see  Stone  block) 
Gravel 

classification,  33 

for    coarse    graded    aggregate 
bituminous  concrete,  225 

concrete      foundations,      174 

gravel  roads,  112 


occurrence,  32 

physical  properties,  34 

production  of,  34 

quality  of  pebbles  in,  329 

roads 

construction  methods,  111 
general  characteristics,  110 
inspector's  equipment  for, 

117 

maintenance,  119 
material  requirements,  112 
measurements,    114 

sampling,  183 

for  gravel  roads,  116 

methods  of,  45 

time  and  place  of,  45 

specification  requirements,  358 

tests 

abrasion,  41 
cementing  value,  42 
elutriation,  42 
field  tests,  113 
size  or  grading,  43 
specific  gravity,  44 
voids,  44 
washing,  42 

types  of,  33 

H 

Hardness  of  rock,  22 
Hardness  test  for  rock,  23 
Highways 

basis  of  measurement,  9 

basis  .Nf  payment,  9 

removal    and   replacement   of 

work,  10 
Hornblende,  17 


Inspection 

bituminous  concrete,  212,  220, 

225,  230,  236 
earth,  244 


368 


Index 


Inspection 

bituminous  macadam,  151 
paving  plants,  189 

surface  treatments,  138 
block  pavements,  250 
brick  pavements,  250 
broken  slag  roads,  121 
broken  stone  roads,  121 
classes  of,  3 

concrete  foundations,  165 
concrete  pavements,  165 
cooperation  of  contractor,  9 
crusher  run  slag  roads,  119 
definition,  1 
details,  10 
gravel  roads,  110 
rock  asphalt,  243 
sand-clay  roads,  103 
sheet  asphalt,  212,  236 
shell  roads,  117 
Topeka  pavements,  230 
Inspector 

paving  plant,  duties  of,  190 
qualifications  of,   1 
relations  of,  5 

to  the  contractor,  7 

to  the  engineer,  5 

to  the  laboratory,  6 
responsibility  of,  2 


H 

Joint  filling,  256 

Joints  expansion,  259 

Joints 

in  brick  pavements,  262 

in  stone  block  pavements,  268 

in  wood  block  pavements,  275 


Lime 

hydrated,  178,  294 
hydraulic,  47 
quick,  47 


Limestone,  13,  14,  19-22 
Limestone,  bituminous,  244 

M 
Macadam,  121 

bituminous,  151 

broken  stone  requirements,  129 

field  tests,  130 

general  methods  of  construc- 
tion,   122 

inspector's  equipment,  137 

maintenance,  135 

measurement,  131 

rock,  126 

spreading  broken  stone,  124 
Marble,  13,  14 
Masonry,  296 
Measurements,  300 

contents  of  tanks,  316 

contents  of  wagons,  314 

linear,  301 

surface,  304 

volume,  312 

weight,  320 

Measures,  equivalent,  321 
Melting  point  test,  94 
Metal  reinforcement,   178,  294 
Mica,  17 

Mineral  filler,  215 
Moisture  in  wood  block,  test  for, 

339 

Mortar,  297 
Mortar  beds,  254 
Mortar  tensile  strength  test  for 
sand,  44 


N 

National  pavement,  245 

Natural  cement, 
classification,  47 
manufacture,  47,  51 
measurement,  55 


Index 


369 


Natural  cement 
properties,  47 
sampling,  56 
specifications,  51 
tensile  strength,  55 
tests,  52 

O 

Oils,  road  (see  also  Petroleum) 

specification  requirements,  359 
Organic  matter  in  sand,  test  for, 

328 


Paints,  297 

Paraffin  scale  determination,  101 

Pat  test,  337 

Paving  plants,  189 

inspection,  196 

inspector's  equipment,  210 

operation  of,  192 

output,  209 

types  of,  190 
Penetration  test,  93,  333 
Peridotite,  13 

Petroleum    (see   also   Bituminous 
materials) 

asphalt  contents  of,  97 

asphalt  from,  64 

blown,  63 

carpeting  mediums,  63,  64,  144 

coefficient  of  expansion,  80 

distillates,  63 

dust  preventives,  63,  143 

emulsifying  oils,  66 

liquid  residues,  63 

products,  63 

sampling,  80 

tests,  86 

topped,  63 

types  of,  62 

volume  of,  77 

weight  of,  73 


Pipes 

clay,  287 
concrete,   288 
metal,  290 
Pitch  fillers,  71 
Portland  cement 
classification,  47 
concrete  (see  Concrete) 
field  tests,  292 
manufacture,  47,  49 
measurement,  55,  180 
properties,   48 
sampling,  56,  183 
specifications,  48 
tests 

chemical  analysis,  52 

fineness,  53 

mortar      tensile     strength 

test,  54 

normal  consistency,  53 
soundness,  54 
specific  gravity,  53 
time  of  setting,  54 
Preservative  coatings,  297 
Puzzolan  cement,  47 

Q 

Quartz,  17 

Quartzite,  13,  14,  19-22 

R 

Reports  and  records 

cost  data,  353 

forms,  354 

inspector's  diary,  353 

paving  plant  operation,  349 

progress  of 'work,  348 

quantities  of  materials,  351 

sampling,  346 
Rhyolite,  13,  14 
Rock 

amphibolite,  13 

andisite,  13,  14 

basalt,  13,  14 


370 


Index 


Rock 

chert,  13,  14,  19 
classification,  12 
conglomerate,  20 
diabase,  13,  14 
diorite,  13,  14 
dolomite,  13,  14,  19-22 
eclogite,  13 
fieldstone,  20 
flint,  13 
gabbro,  13,  14 
gneiss,   13,  14,  18,  20-22 
granite,  13,  14,  18,  20-22 
limestone,  13,  14,  19-22 
marble,  13,  14 
minerals 

augite,  17 

calcite,  18 

dolomite,  18 

feldspars,  17 

hornblende,  17[,m!(, 

mica,  17 

quartz,  17 

rock  glass,  17 
occurrence,  12 
peridotite,  13 
physical  properties,  15 

hardness,  22 

resistance  to  abrasion,  21 

toughness,  22 
quartzite,  13,  14,  19-22 
rhyolite,  13,  14 
sampling,  30 
sandstone,  13,  14,  19-22 
schist,  13,  14,  20 
shale,  13,  14,  20 
slate,  13,  14,  20 
syenite,  13 
tests 

absorption,  25 

cementing  value,  24 

French  coefficient  of  wear, 


22 


hardness,  23 

per  cent  of  wear,  22 

resistance      to      abrasion, 

22 

specific  gravity,  24 
toughness,  23 
trachyte,  13 
trap,  14,  18,  20-22 
Rock  asphalt,  67 
Rock  asphalt  pavements,  243 
Rock  glass,  17 
Rocmac,  298 
Rubble  masonry,  296 

s 

Sand 

classification,  33,  36 

for  binder  course,  237 
bituminous  earth,  245 
concrete  foundation,  176 
concrete  pavement,  177 
coarse  graded  aggregate 

bituminous  concrete,  226 
sheet  asphalt,  238 
Topeka  pavement,  231 

occurrence,  32 

physical  properties,  37 

production  of,  37 

sampling,  45,  183 

tests 

^r   ;  elutriation,  42,i 
grading,  43 
mortar      tensile      strength 

test,  44 

resistance  to  abrasion,  42 
specific  gravity,  44 
voids,  44 
washing,  42 

types  of,  36 
Sand-clay 

classes  of,  105 

fluid  tests,  105 

sampling,  108 


Index 


371 


Sand-clay  roads 

construction  methods,  104 
general  characteristics,  103 
inspector's  equipment,  109 
maintenance,  119 
measurements,  107 
selection  of  materials,  104 
Sand  cushions,  252 
Sandstone,  13,  14,  19-22 
Sandstone,  bituminous,  243 
Schist,  13,  14,  20 
Scoria  block,  266 
Seal  coat,  225,  230 
Shale,.  13,  14,  20 
Sheet     asphalt    pavements     (see 
also    bituminous    aggre- 
gates) 

binder  course,  236 
foundations,  213 
inspector's  equipment,  248 
maintenance,  247 
measurement,  219,  238 
topping,  238 

asphalt  cement,  240 
mix,  241 
sand,  238 
Shell  roads,  117 
Slag,  127 

for  bituminous  Macadam,  156 
coarse  graded  aggregate  bi- 
tuminous concrete,  225 
macadam,  127 

roads  (see  also  Macadam),  119 
Slag  block  pavements,   250,   266 
cushions,   252 
foundations  for,  251 
Slate,  13,  14,  20 
Sodium  silicate,  298 
Specific     gravity     determination, 
24,  44,  53,  88,  330,  342 
Specification  requirements 

asphalt,  for  construction,  361 
asphalt  emulsion,  360 


broken  stone,  357 

creosoting  oils,  362 

gravel,  358 

oils  for  surface  treatment,  359 

sand,  359 

tar,  for  cold  patching,  360 
for  construction,  360 
for  joint  filler,  362 
for  surface  treatment,  360 
Specifications,  scope  of,  8 
Steel,  structural,  296 
Stone  block,  266 

sampling,  270 

size,  267 

tests,  267 

visual  inspection,  268 
Stone  block  pavements,  250,  266 

compaction,  255 

cushions,  252 

foundations  for,  251 

inspector's  equipment,  281 

joint  filling,  256 

joints,  268 

laying,  254 

maintenance,  280 
Subgrade,  preparation  of,  122,  167 
Sulphite  liquors,  299 
Syenite,  13 


Tanks,  capacity  of,  316 
Tar  (see  also  Bituminous  Mate- 
rials) 

carpv.ting  mediums,  70,  144 
coefficient  of  expansion,  80 
creosoting  oils,  71 
dust  preventives,  70,  143 
for  bituminous  macadam,  158 
coarse  graded  aggregate  bi- 
tuminous    concrete,      227 
cold  patching,  360 
construction,  360 
filler,  362 


372 


Index 


Tar 

for    one    size    stone    bitu- 
minous concrete,  221 
surface  treatment,  360 
liquid  refined,  70 
pitch  fillers,  71 
products,  68 
sampling,  80 
semisolid  refined,  70 
tests,  86 
types  of,  68 
volume  of,  76,  77 
weight  of,  73 
Tar     concrete     (see    Bituminous 

concrete) 
Tar    macadam    (see    Bituminous 

Macadam) 

Tar   surface   treatment    (see    Bi- 
tuminous surface  treat- 
ments) 
Telford,  121 

inspector's  equipment,  136 
Tests,  field,  324 

absorption   of   asphalt    block, 

341 

float  test  for  tars,  336 
grading  of  aggregates,  324 
moisture  in  wood  block,  339 
organic  matter  in  sand,  328 
pat  test,  337 

penetration  of  asphalt,  333 
quality  of  gravel  pebbles,  329 
specific  gravity,  330,  342 
voids  in  aggregates,  332 
voids  in  paving  mixtures,  342 
weight  per  cubic  foot,  329 
Thermometers,  testing,  344 
Topeka  pavement,  230 
Topsoil  (see  also  Sand-clay) 
field  tests,  105 
• 


roads,  103 

sampling,  108 

washing  test,  43 
Toughness  of  rock,  21 
Toughness  test  for  rock,  23 
Trachyte,  13 
Trap,  14,  18,  20-22 


Viscosity  test,  91 

Voids,  determination  of,  25,  44, 

332,  342 
Volatilization  test,  96       '•    ! 


W 

Wagons,  capacity  of,  314 
Washing  test  for  gravel,  42 
Wa^te  sulphite  liquors,  299 
Water,  determination    of,  in    bi- 
tuminous materials,  97 

for  concrete,  178 

weight  of,  323 
Water  glass,  298 
Waterproofing  concrete,  294 
Weight  per  cubic  foot  test,  329 
Wood  block,  273 

inspection,  277 

moisture  determination,  339 

requirements,  274 

sampling,  278    . 
Wood  block  pavements,  250,  27'. 

compaction,  255 

foundations  for,  251 

inspector's  equipment,  281 

joint  filling,  256 

joints,  275 

laying,  254 

maintenance,  280 


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